Bumper car is the generic name for a type of amusement ride consisting of several small electric cars that draw their power from an overhead grid, which is turned off by the operator at the end of a session. The metal floor is usually set up as an oval track, and graphite is sprinkled on the floor to decrease friction. A rubber bumper surrounds each vehicle, and drivers ram each other as they travel. The controls are usually an accelerator and a steering wheel. The car can be made to go backwards by turning the steering wheel far enough in either direction, necessary in the frequent pile-ups that occur.
Although the idea of the ride is to bump other cars, safety-conscious (or at least litigation-conscious) owners often put up signs reading "This way round" and "No bumping".
During their heyday (late 1920s through 1950s), the two major bumper car brands were Dodgem and the Lusse Brothers' Auto-Skooter. In the mid 1960s, Disneyland introduced hovercraft-based bumper cars called "The Flying Saucers," which worked on the same principle as an air-hockey rink; the ride was a mechanical failure and closed after a few years.
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A list of amusement ride patents, including bumper cars, with links to the U.S. Patent office: