A bicycle, often called a bike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A bicycle rider is called a cyclist, or bicyclist.\nBicycles were introduced in the 19th century in Europe and, as of 2003, number more than a billion worldwide, twice as many as automobiles. They are the principal means of transportation in many regions. They also provide a popular form of recreation, and have been adapted for use as children\'s toys, general fitness, military and police applications, courier services, and bicycle racing.\nThe basic shape and configuration of a typical upright, or safety bicycle, has changed little since the first chain-driven model was developed around 1885. \nThe bicycle\'s invention has had an enormous effect on society, both in terms of culture and of advancing modern industrial methods. Several components that eventually played a key role in the development of the automobile were initially invented for use in the bicycle, including ball bearings, pneumatic tires, chain-driven sprockets, and tension-spoked wheels.