a compressor used to increase the density of the air or mixture supplied to an engine. Normally driven either by the engine or by an exhaust turbine, An engine or exhaust driven air compressor used to provide additional pressure to the induction air so the engine can produce additional power., device such as a positive displacement compressor or dynamic compressor used to improve the volumetric efficiency and power output of internal combustion engines by raising the intake pressure, ths increasing the amount of air drawn in (NOTE: largely superseded in cars by the turbocharger)