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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. Invented in Europe in the 19th century, the bicycle has become the world's most popular vehicle with about 1.4 billion in use.
In addition to transport, bicycles 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.
 Uses for bicycles
Bicycles have been and are employed for many uses.
- Utility: bicycle commuting and utility cycling
- Work: mail delivery, paramedics, police, and general delivery.
- Recreation: bicycle touring, mountain biking, BMX and physical fitness.
- Racing: track racing, criterium, roller racing and time trial to multi-stage events like the Tour of California, Giro d'Italia, the Tour de France, and the Vuelta a España.
- Military: scouting, troop movement, supply of provisions, and patrol.
- Show: entertainment and performance, e.g. circus clowns
 Technical aspects
 Types of bicycles
These are the main types of bicycles :
- Utility bicycles (race, mountain, touring)
- Race bicycles
- Mountain bicycles
- Touring bicycles
- Cruiser bicycles
- BMX bicycles
- Recumbent bicycles (laid down position)
- Tall bikes
- Fixed-gear bicycles
- Folding bicycles
- Unicycles, Tricycle and Quadricycles (even though they're not bicycles properly speaking)