Plain English Meaning

A basic supercharger that helps the engine make full power at low altitudes, but loses effectiveness as the airplane climbs higher. It can keep the engine acting like it is at sea level only for a short way up; after that, power falls off the same way it would in an unsupercharged engine.

Full Definition

A single-stage, single-speed engine-driven supercharger designed to maintain sea-level manifold pressure only up to a relatively low altitude. Above its rated altitude, manifold pressure and engine power drop off as ambient air density continues to decrease, because the supercharger cannot compress the thinner enough to maintain sea-level output.