A unicycle is a pedal-powered vehicle with only one wheel (or at least only one that touches the ground). Unlike a bicycle, the wheel of a unicycle is directly controlled by the pedals, which makes it possible to ride backwards and to idle (pedal back and forth to stay balanced in one place), and also makes it impossible to coast without taking the feet off the pedals.
Types of unicycles include the giraffe (a tall, chain-driven unicycle), the ultimate wheel (no seat), and the impossible wheel (no seat and no pedals).
