What is a Möbius strip?

The Möbius strip was described independently in 1858 by German mathematicians August Ferdinand Möbius and Johann Benedict Listing. If you draw a line along the middle of the strip, you return to your starting point having covered both 'sides' without lifting your pen, proving it has only one surface. Cutting it lengthways down the middle does not produce two loops but one longer loop with extra twists. It is a key example in topology, the maths of shapes that can be stretched and bent. The strip has practical uses too, such as conveyor belts designed to wear evenly on both faces.