A mechanically driven air compressor used to increase engine power is called a supercharger.
A supercharger compresses the air entering an internal-combustion engine. Denser intake air allows the cylinders to burn more fuel while maintaining the correct air-fuel ratio, increasing power from a given engine displacement. Traditional superchargers are powered mechanically, commonly by a belt connected to the crankshaft; some newer versions use gears, chains, or an electric motor.
Supercharging has roots in late-19th-century compressor experiments, and aircraft engines adopted it widely during the 1910s to compensate for thin air at high altitude. Automobile use expanded in the 1920s. Roots, twin-screw, and centrifugal designs remain familiar types, each compressing or moving intake air differently.
The common mix-up is turbocharger. Both systems provide forced induction, but a conventional supercharger takes power from the engine mechanically, while a turbocharger uses exhaust-gas energy to spin its turbine. That difference affects response, efficiency, packaging, and sound.