An impeller is a drive system for a boat that uses a pump to pressurize water for thrust rather than using a propeller. Since an impeller does not have blades that have to displace water for the craft to move, it can reach much higher speeds than a traditional outboard.
Inside an impeller is a centrifugal pump, which contains a grooved disk. Water flows into the pump, and the disk spins at high speeds, forcing water outward with centrifugal force. The water is held in by the pump housing and forced out the rear of the impeller, pushing the craft forward.