A bicycle is a bipedal person-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. Since their creation, bicycles have been and are employed for many uses. In a utilitarian way, bicycles are used for transportation, bicycle commuting, and utility cycling. It can be used as a 'work horse', used by mail carriers, paramedics, police, messengers, and general delivery services. Military uses of bicycles include communications, reconnaissance, troop movement, supply of provisions, and patrol as part of a bicycle infantry. The bicycle is also used for recreational purposes, such as bicycle touring, mountain biking, physical fitness, and play. Bicycle competition includes racing, BMX racing, track racing, time trials, and major multi-stage professional events. Bikes can be used for entertainment and pleasure, such as in organized mass rides, artistic cycling and freestyle BMX.