A bicycle, often called a bike (and sometimes referred to as a “pushbike”, “pedal bike”, “pedal cycle”, or “cycle”), is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist. Bicycles were introduced in the 19th century in Europe and now number more than a billion worldwide, twice as many as automobiles. They are the principal means of transportation in many regions.