A child's tricycle is best known, but adult tricycles are becoming more common. The adult trikes will have a chain, gears and are recumbent (the feet are in front of the body). They come in two main styles: tadpole with two wheels up front and one in back and delta with two wheels in the back and one wheel in the front. Almost always the front wheel or wheels steer the bike, and power goes to the back wheel or wheels.
Some trikes are fully faired (covered in a shell to cut wind resistance). These are called velomobiles.