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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.
Bicycles were introduced in the 19th century in Europe and, as of 2003, more than a billion have been produced worldwide, twice as many as the number of automobiles that have been produced. They are the principal means of transportation in many regions.