What

The skin is the largest organ, covering 1.5–2 square meters in adults and weighing about 3.6 kg. It has three layers: epidermis, dermis, and hypodermis.

Light travels at exactly 299,792,458 meters per second in a vacuum — about 1.08 billion km/h. One light-year equals 9.46 trillion km, and sunlight takes 8 minutes 20 seconds to reach Earth.

DNA (deoxyribonucleic acid) is the molecule that stores genetic instructions in every living cell. Human DNA contains about 3 billion base pairs and is 99.9% identical between any two people.

The Challenger Deep in the Mariana Trench reaches 11,034 meters (36,201 feet) below sea level — deeper than Mount Everest is tall. Only three crewed descents have reached the bottom.

Venus is the hottest planet at 465°C (869°F) average surface temperature — hotter than Mercury despite being nearly twice as far from the Sun. Its thick CO₂ atmosphere creates a runaway greenhouse effect.

Mandarin Chinese has the most native speakers (~920 million), but English is the most widely spoken overall (~1.5 billion speakers including non-native). Spanish ranks third with ~550 million total speakers.

The Milky Way is our home galaxy — a barred spiral galaxy about 100,000 light-years in diameter containing 200–400 billion stars. Our Solar System sits about 26,000 light-years from the galactic center.

Vatican City is the smallest country by both area (0.44 sq km) and population (~800 citizens). It is an independent city-state entirely surrounded by Rome, Italy.

A black hole is a region where gravity is so strong that nothing, not even light, can escape. Its boundary is the event horizon; at the center lies a singularity.

Gravity is the attractive force between all objects with mass. Einstein described it not as a force but as the curving of spacetime caused by mass and energy.

Evolution is the change in the heritable traits of populations over successive generations, driven largely by natural selection. It explains the diversity of all life on Earth.

Absolute zero is the coldest possible temperature, −273.15°C (0 Kelvin), where atomic motion reaches its minimum. It can be approached but never fully reached.

The Higgs boson is a fundamental particle linked to the field that gives other particles mass. It was discovered at CERN in 2012, confirming a 1964 prediction.

Photosynthesis is how plants, algae, and some bacteria turn sunlight, water, and carbon dioxide into glucose and oxygen. It powers nearly all life on Earth.

A light-year is the distance light travels in one year — about 9.46 trillion kilometers. It is a measure of distance, not time.

The human genome is the complete set of DNA instructions for a person — about 3 billion base pairs and roughly 20,000 protein-coding genes. It was first fully sequenced in 2003.

Antimatter is made of particles with the opposite charge to ordinary matter. When matter and antimatter meet, they annihilate in a burst of pure energy.

The Fibonacci sequence is a series where each number is the sum of the two before it: 0, 1, 1, 2, 3, 5, 8, 13… It appears throughout nature and links to the golden ratio.

A supernova is the colossal explosion of a dying star, briefly outshining an entire galaxy and forging heavy elements.

An atom is the basic building block of matter, made of a dense nucleus of protons and neutrons surrounded by electrons.

A virus is a tiny infectious agent that can only reproduce inside a living cell. It sits at the boundary between living and non-living.

Climate change is the long-term shift in global temperatures and weather patterns, driven mainly by human greenhouse-gas emissions.

Electricity is the flow of electric charge, usually carried by electrons moving through a material such as a metal wire.

The immune system is the body defence network that detects and destroys harmful invaders like bacteria, viruses, and abnormal cells.

A galaxy is a vast system of stars, gas, dust, and dark matter bound together by gravity. The observable universe holds hundreds of billions of them.

Artificial intelligence is the field of building machines and software that can perform tasks that normally require human intelligence.

The water cycle is the continuous movement of water through evaporation, condensation, and precipitation across Earth.

A tsunami is a series of huge ocean waves, usually caused by an undersea earthquake, that can travel across whole oceans at jet speed.

A vaccine is a preparation that trains the immune system to recognise and fight a specific germ without causing the disease itself.

The periodic table is an organised chart of all known chemical elements, arranged by their atomic number and shared properties.

A comet is a small icy body that grows a glowing coma and tail when it nears the Sun and its ices vaporise.

Sound is a wave of vibrations travelling through a medium like air or water. It cannot travel through the vacuum of space.

A cell is the smallest unit of life. Every living thing is made of one or more cells, from single-celled microbes to humans.

A neutron star is the ultra-dense collapsed core of a massive star that exploded as a supernova.

Plate tectonics is the theory that Earth outer shell is divided into large moving plates whose interactions cause earthquakes, volcanoes, and mountain building.

An enzyme is a biological catalyst — usually a protein — that speeds up chemical reactions in living organisms without being consumed.

Dark matter is an invisible substance that makes up about 27% of the universe and exerts gravitational pull but does not emit or absorb light.

A prion is a misfolded protein that can cause other normal proteins to misfold, leading to fatal brain diseases.

The ozone layer is a region of the stratosphere, 15 to 35 km above Earth, where concentrated ozone (O₃) absorbs most of the Sun harmful UV-B and UV-C radiation.

The gut microbiome is the vast community of trillions of microorganisms living in the human digestive tract that aid digestion, immunity, and even mood.

A solar eclipse occurs when the Moon passes directly between the Sun and Earth, casting a shadow on our planet.

CRISPR is a gene-editing technology that allows scientists to precisely cut and modify DNA sequences in living organisms.

Plasma is the fourth state of matter — an ionised gas where atoms have lost electrons, making it electrically conductive.

Radiocarbon dating measures the decay of carbon-14 in organic material to estimate how long ago a living thing died.

Bioluminescence is the production of light by living organisms through a chemical reaction involving the molecule luciferin.

A semiconductor is a material whose electrical conductivity falls between that of a conductor and an insulator, and can be controlled by doping or voltage.

An aurora is a natural light display in the sky caused by charged particles from the Sun colliding with gases in Earth atmosphere.

A black body is an idealised object that absorbs all incoming electromagnetic radiation and re-emits it based solely on its temperature.

A quasar is an extremely luminous active galactic nucleus powered by a supermassive black hole devouring surrounding material.

An ecosystem is a community of living organisms interacting with each other and their physical environment as a functional unit.

The Doppler effect is the change in frequency of a wave as the source and observer move relative to each other.

A coral reef is an underwater ecosystem built by colonies of tiny animals (coral polyps) that secrete calcium carbonate skeletons over thousands of years.

A blockchain is a decentralised, tamper-resistant digital ledger that records transactions across many computers so no single entity controls the data.

A hormone is a chemical messenger produced by endocrine glands that travels through the blood to regulate distant organs and body processes.

A superconductor is a material that conducts electricity with zero resistance when cooled below a critical temperature.

6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂ — carbon dioxide and water are converted into glucose and oxygen using sunlight.

Isotopes are variants of a chemical element that share the same number of protons but differ in their neutron count, giving them different atomic masses.

A neutrino is an electrically neutral, nearly massless subatomic particle that interacts with matter only through the weak nuclear force and gravity, making it extraordinarily difficult to detect.

The greenhouse effect is the natural warming of Earth surface caused by atmospheric gases trapping heat that would otherwise escape to space.

A meteoroid is a space rock; a meteor is the streak of light it creates in Earth atmosphere; a meteorite is the piece that survives to reach the ground.

The event horizon is the boundary around a black hole beyond which nothing — not even light — can escape.

Entropy is a measure of disorder or randomness in a system; the second law of thermodynamics states that entropy in an isolated system always increases.

A prism is a transparent optical element with flat, polished surfaces that refracts light, splitting white light into its constituent colours.

A pulsar is a rapidly spinning neutron star that emits beams of electromagnetic radiation from its magnetic poles; as the star rotates, these beams sweep across space like a lighthouse.

A tectonic plate is a massive slab of Earth lithosphere — crust and upper mantle — that floats on the semi-fluid asthenosphere and moves a few centimetres per year, driving earthquakes, volcanoes, and mountain building.

A supermassive black hole is a black hole with a mass of millions to billions of times that of the Sun, found at the centre of most large galaxies, including our Milky Way.

An alloy is a metallic material made by combining two or more elements (at least one a metal) to achieve properties — such as strength, corrosion resistance, or hardness — superior to the individual components.

A biome is a large-scale ecological community defined by its dominant vegetation, climate, and wildlife — examples include tropical rainforests, deserts, tundra, and grasslands.

Surface tension is the elastic-like force at the surface of a liquid, caused by cohesive forces between molecules pulling surface molecules inward, making the surface behave like a stretched membrane.

A catalyst is a substance that speeds up a chemical reaction without being permanently consumed, by lowering the activation energy needed for the reaction to proceed.

The Coriolis effect is the apparent deflection of moving objects (like wind and ocean currents) caused by Earth rotation — to the right in the Northern Hemisphere and to the left in the Southern.

Epigenetics is the study of heritable changes in gene expression that do not involve alterations to the DNA sequence itself — modifications that turn genes on or off without changing the genetic code.

Probiotics are live microorganisms — mainly bacteria and yeasts — that, when consumed in adequate amounts, confer a health benefit on the host by supporting the gut microbiome.

A dwarf planet is a celestial body that orbits the Sun, has sufficient mass for gravity to pull it into a roughly spherical shape, but has not "cleared the neighbourhood" around its orbit of other debris.

Absolute humidity is the total mass of water vapour present in a given volume of air, measured in grams per cubic metre, regardless of temperature.

A lichen is a composite organism formed by a symbiotic partnership between a fungus and one or more photosynthetic partners (green algae or cyanobacteria), functioning as a single ecological unit.

Permafrost is ground that remains frozen (at or below 0 degrees Celsius) continuously for at least two consecutive years, found beneath about 15% of the Northern Hemisphere land surface.

The Heisenberg uncertainty principle states that it is fundamentally impossible to simultaneously know both the exact position and exact momentum of a particle with arbitrary precision.

The aurora borealis (northern lights) is a natural light display caused by charged particles from the Sun colliding with atmospheric gases along Earth magnetic field lines near the poles, making oxygen and nitrogen glow.

Tardigrades ("water bears") are microscopic eight-legged animals, typically 0.1-1.5 mm long, famous for being the most resilient animals known — they can survive extreme temperatures, radiation, vacuum of space, and pressures that would destroy most life.

A piezoelectric material generates an electrical charge when mechanically stressed (squeezed, bent, or vibrated), and conversely changes shape when an electric field is applied — a direct coupling between mechanical and electrical energy.

Microplastics are tiny plastic particles less than 5 mm in diameter that result from the breakdown of larger plastic items, industrial processes, and synthetic textiles — they are now found in every environment on Earth, from deep ocean sediments to human blood.

A neutron bomb (enhanced radiation weapon) is a type of thermonuclear weapon designed to maximise lethal neutron radiation while minimising blast and thermal destruction — intended to kill personnel while leaving structures relatively intact.

Mycelium is the vast underground network of thread-like filaments (hyphae) that forms the main body of a fungus — mushrooms are just the visible fruiting bodies of this hidden network, which can span kilometres.

A rogue wave is an unexpectedly large ocean wave — at least twice the height of surrounding waves — that appears suddenly and can be catastrophically dangerous to ships, once dismissed as sailor myth but now scientifically confirmed.

A qubit (quantum bit) is the basic unit of quantum information, analogous to a classical bit but capable of existing in a superposition of both 0 and 1 simultaneously, enabling quantum computers to process certain problems exponentially faster.

Albedo is the fraction of incoming solar radiation that a surface reflects back into space, ranging from 0 (absorbs all light) to 1 (reflects all light) — it is a key factor in Earth energy balance and climate.

A geode is a rounded hollow rock lined with crystals (usually quartz or amethyst) on the inside — formed when mineral-rich water seeps into a gas bubble or cavity in volcanic or sedimentary rock and slowly deposits crystals over millions of years.

A keystone species is an organism that has a disproportionately large effect on its ecosystem relative to its abundance — its removal would cause dramatic changes or even collapse of the ecosystem.

Sonoluminescence is the mysterious phenomenon where sound waves in liquid cause tiny bubbles to collapse so violently that they emit brief flashes of light, reaching temperatures potentially exceeding 20,000 Kelvin.

A wetland is an area where water covers the soil or is present at or near the surface for at least part of the year — including marshes, swamps, bogs, and fens — making them among the most biologically productive ecosystems on Earth.

Electromagnetic induction is the generation of an electric current in a conductor by a changing magnetic field — the principle behind electric generators, transformers, and induction charging, discovered by Michael Faraday in 1831.

Fullerenes are hollow cage-shaped molecules made entirely of carbon atoms — the most famous being C60 (buckminsterfullerene or "buckyball"), a sphere of 60 carbon atoms arranged like a soccer ball, discovered in 1985.

Quantum entanglement is a phenomenon in which two or more particles become linked so that measuring the state of one instantly determines the state of the other, no matter how far apart they are.

The placebo effect is a real, measurable improvement in a person condition after receiving an inactive treatment, driven by their expectation and belief that the treatment will help.

A glacier is a large, persistent mass of ice that forms on land from compacted snow over many years and flows slowly under its own weight, reshaping landscapes as it moves.

A nebula is a vast interstellar cloud of gas and dust, often spanning many light-years, that can serve as a stellar nursery where new stars form or as the glowing remnant of a dying star.

Osmosis is the movement of water molecules across a semipermeable membrane from a region of lower solute concentration to a region of higher solute concentration, equalising the concentration on both sides.

The Richter scale measures the magnitude of earthquakes on a logarithmic scale.

A meteor is the streak of light made when a space rock burns up in Earths atmosphere.

A hurricane is a powerful tropical storm with a spiralling structure and a calm central eye.

Inflation is the general rise in prices of goods and services over time, which reduces the purchasing power of money; a moderate, steady inflation rate (around 2%) is generally considered healthy for an economy.

Condensation is the process by which a gas turns into a liquid, such as water vapour forming droplets.

A fossil is the preserved remains or traces of a once-living organism from the distant past.

The pH scale measures how acidic or alkaline a solution is, running from 0 to 14.

A tsunami is a series of enormous ocean waves usually caused by underwater earthquakes, volcanic eruptions, or landslides that displace huge volumes of water; in the open ocean they are barely noticeable, but they grow into towering, destructive waves near shore.

A genetic mutation is a change in the DNA sequence of an organism; mutations can be harmful, beneficial, or neutral, and they are the ultimate source of the genetic variation that drives evolution by natural selection.

A tornado is a violently rotating column of air reaching from a thunderstorm to the ground.

A blood type is a classification of blood based on the presence or absence of specific molecules called antigens on the surface of red blood cells, most importantly the ABO and Rh systems.

A food chain is a sequence showing how energy and nutrients pass from one living thing to another as each organism eats the one before it, starting with producers like plants and moving up to predators.

A hologram is a three-dimensional image created by recording the pattern of light waves reflected from an object, so the image appears to have depth and changes as you view it from different angles.

A solar flare is a sudden, intense burst of radiation from the Sun, released when magnetic energy stored in its atmosphere is explosively unleashed, often near sunspots.

A tectonic fault is a fracture or zone of fractures in the Earth crust where blocks of rock have moved relative to each other; sudden slips along faults are what cause most earthquakes.

Carbon dating is a method for estimating the age of once-living material by measuring how much of the radioactive isotope carbon-14 remains, since it decays at a known, steady rate after death.

Cryptocurrency is a form of digital money that uses cryptography for security and typically runs on a decentralised ledger called a blockchain, allowing transactions without a central bank or government.

Dark energy is a mysterious form of energy thought to make up about 68 percent of the universe and to be responsible for driving its accelerating expansion.

Inflation is the general rise in prices over time, which reduces the purchasing power of money — meaning each unit of currency buys fewer goods and services than before.

Nuclear fusion is the process of forcing light atomic nuclei to merge into a heavier one, releasing enormous energy; it is the reaction that powers the Sun and other stars.

Radioactivity is the process by which unstable atomic nuclei lose energy by emitting radiation — such as alpha particles, beta particles, or gamma rays — as they transform into more stable forms.

Static electricity is an imbalance of electric charge that builds up on the surface of a material, usually created by friction, and is released as a spark or shock when it finds a path to discharge.

The electromagnetic spectrum is the full range of electromagnetic waves, from long-wavelength radio waves to short-wavelength gamma rays, with visible light making up only a tiny portion in the middle.

The internet is a vast global network of interconnected computers that communicate using shared protocols, allowing information to be exchanged between billions of devices around the world.

The jet stream is a fast, narrow band of high-altitude wind that flows from west to east around the planet, strongly influencing weather patterns and the routes of aircraft.

A caldera is a large, cauldron-like hollow that forms when a volcano collapses into its own emptied magma chamber after a massive eruption.

A coral polyp is a tiny soft-bodied marine animal that builds a hard skeleton; vast colonies of these polyps create coral reefs.

A cumulonimbus is a towering, dense storm cloud that can reach great heights and produces thunderstorms, heavy rain, lightning, hail, and sometimes tornadoes.

A fjord is a long, deep, narrow inlet of the sea carved by glaciers and flanked by steep cliffs, formed when the ocean floods a glacial valley.

A geyser is a hot spring that periodically erupts, shooting a column of boiling water and steam into the air when underground water is superheated by volcanic rock.

A moraine is a ridge or mound of rock and debris that a glacier picks up, carries, and deposits as it flows and later melts.

A limestone cave is an underground cavern dissolved out of limestone rock by slightly acidic water over thousands of years, often decorated with stalactites and stalagmites.

A lunar eclipse occurs when Earth passes directly between the Sun and the Moon, casting its shadow on the Moon and often turning it a coppery red.

A magnetar is a type of neutron star with an extraordinarily powerful magnetic field, the strongest known in the universe, capable of releasing enormous bursts of energy.

A mangrove forest is a coastal woodland of salt-tolerant trees that grow in tidal saltwater, with tangled roots that protect shorelines and shelter marine life.

A monsoon is a seasonal reversal of wind that brings a dramatic shift between wet and dry periods, most famously the heavy summer rains across South Asia.

A peninsula is a piece of land almost entirely surrounded by water but still connected to a larger landmass by a narrow strip called an isthmus.

A savanna is a tropical grassland biome dotted with scattered trees, defined by warm temperatures and a strong split between wet and dry seasons.

A sinkhole is a hole or depression in the ground that forms when underlying rock is dissolved away or an underground cavity collapses, sometimes suddenly and dramatically.

A stalactite is an icicle-shaped mineral formation that hangs from the ceiling of a cave, built up drop by drop from mineral-rich dripping water.

A storm surge is an abnormal rise of seawater pushed ashore by a storm strong winds and low pressure, often causing the deadliest flooding in hurricanes.

A tidal bore is a wave or wall of water that travels upstream against a river current when a strong incoming tide surges into a narrowing estuary.

The tundra is a cold, treeless biome with a short growing season and frozen subsoil called permafrost, found in the far north and on high mountains.

An oxbow lake is a curved, crescent-shaped lake formed when a loop of a meandering river is cut off from the main channel.

A blue moon is an extra full moon in a period, usually the second full moon in a single calendar month, and it is not actually blue in colour.

A VPN, or virtual private network, creates an encrypted tunnel between your device and a remote server, hiding your internet traffic from local networks and masking your IP address.

Cloud computing means renting computing power, storage and software over the internet from large data centres instead of owning and running the hardware yourself.

5G is the fifth generation of mobile network technology, offering much faster data speeds, lower delay and the ability to connect far more devices than 4G.

An IP address is a unique numerical label assigned to each device on a network, allowing data to be sent to the right place across the internet.

An algorithm is a precise, step-by-step set of instructions for solving a problem or completing a task, used by computers for everything from searching to recommending videos.

A recession is a significant, widespread decline in economic activity lasting months, often marked by falling output, rising unemployment and weaker spending.

The stock market is a network of exchanges where investors buy and sell shares, small pieces of ownership in public companies.

A large language model is an AI system trained on vast amounts of text to predict the next word in a sequence, allowing it to answer questions, write and summarise in natural language.

Machine learning is a branch of artificial intelligence in which computers learn patterns from data and improve at tasks without being explicitly programmed for each step.

Malware, short for malicious software, is any program designed to harm, spy on or take control of computers, including viruses, worms, ransomware and spyware.

Augmented reality overlays digital images, text or sounds onto a live view of the real world, usually through a phone camera or smart glasses.

GDP, or gross domestic product, is the total market value of all finished goods and services produced within a country in a given period, usually a year or quarter.

A credit score is a number that estimates how likely a person is to repay borrowed money, based on their history of loans, credit cards and bill payments.

An NFT, or non-fungible token, is a unique digital record on a blockchain that proves ownership of a specific item, such as a piece of digital art.

A pandemic is an outbreak of a new or re-emerging disease that spreads across multiple countries or continents, affecting a large number of people.

Cholesterol is a waxy, fat-like substance that the body needs to build cells and make hormones, but too much of certain types in the blood can clog arteries.

A calorie is a unit of energy; the food Calorie on nutrition labels is a kilocalorie, the energy needed to raise one kilogram of water by one degree Celsius.

Diabetes is a long-term condition in which blood sugar levels are too high because the body cannot make enough insulin or cannot use it properly.

A QR code is a square two-dimensional barcode that stores information such as a web link, which a phone camera can read instantly.

El Niño is a natural climate pattern in which the surface waters of the central and eastern tropical Pacific become unusually warm, shifting weather around the world.

The Big Bang is the scientific theory that the universe began about 13.8 billion years ago from an extremely hot, dense state and has been expanding and cooling ever since.

ADHD, or attention-deficit/hyperactivity disorder, is a common neurodevelopmental condition marked by ongoing patterns of inattention, hyperactivity and impulsivity.

A meme is an idea, joke or image that spreads from person to person and changes as it goes; the word was coined by biologist Richard Dawkins in 1976.

An API, or application programming interface, is a set of rules that lets one piece of software request data or services from another without knowing how it works inside.

Phishing is a scam in which criminals send fake emails, texts or calls pretending to be a trusted organisation to trick people into revealing passwords, money or personal information.

The keto diet is a very low-carbohydrate, high-fat eating plan that pushes the body into ketosis, a state where it burns fat and produces ketones for fuel instead of relying on sugar.

Intermittent fasting is an eating pattern that cycles between periods of eating and fasting, such as eating only within an eight-hour window each day.

Ozempic is a brand of semaglutide, a weekly injectable drug that mimics the gut hormone GLP-1 to lower blood sugar and reduce appetite; it is approved for type 2 diabetes, and a higher-dose version is sold for weight loss.

Dopamine is a chemical messenger in the brain that drives motivation, reward-seeking, learning and movement, rather than simply producing pleasure.

Black Friday is the day after Thanksgiving in the United States, traditionally the start of the Christmas shopping season and famous for huge discounts.

Compound interest is interest earned on both your original money and on the interest it has already earned, so savings or debts grow faster and faster over time.

Scientists describe romantic love as a set of brain systems for lust, attraction and attachment, driven by chemicals such as dopamine, oxytocin and vasopressin.

A migraine is a neurological condition that causes intense, often one-sided throbbing headaches lasting hours to days, frequently with nausea and sensitivity to light and sound.

The dark web is a small, hidden part of the internet that search engines cannot index and that can only be reached with special software such as the Tor browser, which hides users identities.

A deepfake is a video, image or audio clip created or altered with artificial intelligence to make someone appear to say or do something they never did.

The metaverse is the idea of shared, persistent 3D virtual worlds where people meet, work, play and trade, often using virtual or augmented reality.

IQ, or intelligence quotient, is a score from standardised tests of reasoning and problem-solving. Tests are set so the average score is 100.

Anxiety is the body’s natural response to perceived threat, causing worry, a racing heart and tension. When it is intense and persistent, it can become an anxiety disorder.

Gluten is a group of proteins found in wheat, barley and rye. It makes dough stretchy and helps bread rise.

Autism is a lifelong neurodevelopmental difference that affects how people communicate, interact and experience the world. It is a spectrum, so it varies widely from person to person.

Vitamin D is a nutrient the skin makes when exposed to sunlight. It helps the body absorb calcium and keeps bones and muscles healthy.

Gaslighting is a form of psychological manipulation in which someone makes another person doubt their own memory, perception or sanity.

Quantum computers use qubits that can exist in combinations of 0 and 1 at once. For certain problems, this could let them solve tasks far beyond ordinary computers.

Veganism is a way of living that avoids animal products, including meat, fish, dairy, eggs and honey, and often leather and wool too.

Stoicism is an ancient Greek philosophy that teaches people to focus on what they can control, accept what they cannot, and live by virtue.

Mindfulness means paying full attention to the present moment, on purpose and without judgment. It is often practised through meditation.

Narcissism is excessive self-focus, including a need for admiration and a lack of empathy. In its extreme form it is diagnosed as narcissistic personality disorder.

Sleep paralysis is being awake but temporarily unable to move or speak while falling asleep or waking up. It often comes with vivid, frightening hallucinations.

Umami is the fifth basic taste, alongside sweet, sour, salty and bitter. It is a savoury, meaty flavour caused mainly by glutamate.

A carbon footprint is the total amount of greenhouse gases caused by a person, product or organisation, usually measured in tonnes of carbon dioxide equivalent.

A hashtag is a word or phrase after a # symbol that groups social media posts on the same topic.

The Turing test checks whether a machine can hold a conversation indistinguishable from a human’s.

A leap second is an extra second occasionally added to clocks to keep atomic time in line with Earth’s rotation.

The Mandela effect is when many people share the same false memory of an event or detail.

FOMO, or fear of missing out, is anxiety that others are having rewarding experiences without you.

The butterfly effect is the idea that tiny changes in a complex system can lead to huge differences later.

It is a 1935 thought experiment showing how strange quantum rules seem when applied to everyday objects.

A mortgage is a loan used to buy property, where the property itself serves as security for the loan.

An index fund is an investment fund that tracks a market index, such as the S&P 500, instead of picking stocks.

A central bank manages a country’s money supply and interest rates and oversees the banking system.

It is a 2015 international treaty in which countries agreed to limit global warming to well below 2°C.

Net zero means cutting greenhouse gas emissions as far as possible and balancing the rest by removing an equal amount.

The polar vortex is a large area of cold, swirling air high above each pole that can spill south and bring freezing weather.

The Kuiper Belt is a vast ring of icy bodies beyond Neptune, home to dwarf planets such as Pluto.

A red giant is a dying star that has swollen to enormous size after running low on hydrogen in its core.

A white dwarf is the hot, dense core left behind after a Sun-like star dies.

An exoplanet is a planet that orbits a star other than our Sun.

A sonic boom is the thunder-like sound created by shock waves when an object travels faster than sound.

The golden ratio is about 1.618, a proportion where the whole relates to the larger part as the larger part relates to the smaller.

Pi (π) is the ratio of a circle’s circumference to its diameter, about 3.14159.

A prime number is a whole number greater than 1 that can be divided evenly only by 1 and itself.

Infinity is the idea of something without any end or limit, larger than any number.

A googol is 1 followed by 100 zeros, or 10 to the power of 100.

In a right-angled triangle, the square of the longest side equals the sum of the squares of the other two: a² + b² = c².

Cookies are small text files websites store in your browser to remember logins, settings and browsing activity.

Two-factor authentication (2FA) requires a second proof of identity, like a code or fingerprint, in addition to a password.

Ransomware is malicious software that locks or encrypts a victim’s files and demands payment to unlock them.

Open-source software has source code that anyone can freely view, use, modify and share.

A pixel is the smallest dot of colour that makes up a digital image or screen.

A gigabyte is a unit of digital storage equal to about one billion bytes.

A watt is the unit of power, measuring how fast energy is used or produced: one joule per second.

Serotonin is a chemical messenger involved in mood, sleep, digestion and many other body functions.

Melatonin is a hormone that signals darkness to the body and helps regulate the sleep–wake cycle.

Cortisol is a hormone made by the adrenal glands that helps the body respond to stress and regulates energy.

Adrenaline is a hormone released in moments of danger or excitement that prepares the body for fight or flight.

Body mass index (BMI) is weight in kilograms divided by height in metres squared, used as a rough health screen.

Dietary fibre is the part of plant foods the body cannot digest, which aids digestion and feeds gut bacteria.

It is an eating pattern rich in vegetables, fruit, whole grains, legumes, fish and olive oil, inspired by Mediterranean countries.

A concussion is a mild traumatic brain injury caused by a blow or jolt that shakes the brain inside the skull.

A stroke happens when blood supply to part of the brain is blocked or a blood vessel bursts, damaging brain cells.

Blood pressure is the force of blood pushing against artery walls, written as two numbers such as 120/80.

Sleep apnea is a disorder in which breathing repeatedly stops and starts during sleep.

Democracy is a system of government where power rests with the people, who rule directly or through elected representatives.

NATO is a military alliance of North American and European countries that pledge to defend each other.

The European Union is a political and economic union of 27 European countries sharing a single market and common rules.

A haiku is a short Japanese poem, traditionally of three lines with 5, 7 and 5 sound units.

A palindrome is a word, phrase or number that reads the same backwards as forwards.

Morse code represents letters and numbers with patterns of short and long signals, called dots and dashes.

The Great Red Spot is a giant storm on Jupiter, wider than Earth, that has raged for at least 190 years.

A wormhole is a theoretical tunnel through spacetime that could connect two distant points in the universe.