Bicycles

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The bicycle, bike, or cycle, is a pedal-driven, human-powered vehicle with two wheels attached to a frame, one behind the other.

First introduced in 19th-century Europe, bicycles now number approximately one billion worldwide, providing the principal means of transportation in many regions, notably China and the Netherlands. They also provide a popular form of recreation, and have been adapted for use in many other fields of human activity, including children's toys, adult fitness, military and police applications, courier services, and cycle sports.

The basic shape and configuration of a typical bicycle has hardly changed since the first chain-driven model was developed around 1885, although many important details have been improved, especially since the advent of modern materials and computer-aided design. These have allowed for a proliferation of specialized designs for particular types of cycling.