What Is a Blockchain?

A blockchain is a chain of "blocks," each containing a batch of verified transactions. Each block includes a cryptographic hash of the previous block, a timestamp, and transaction data. This chaining makes the ledger tamper-resistant: altering one block would change its hash, breaking the chain and alerting the network. In public blockchains like Bitcoin, thousands of computers (nodes) maintain copies of the ledger and use consensus mechanisms (proof of work or proof of stake) to agree on valid transactions without a central authority. Beyond cryptocurrency, blockchain technology is used for supply-chain tracking, digital identity, smart contracts, and decentralised finance (DeFi).