Plain English Meaning

The faster of two gear settings on an engine's built-in air pump. Switching to high blower spins the pump harder so the engine can keep making power when the air gets thin at altitude.

Full Definition

The high-speed setting of a two-speed internal supercharger fitted to certain reciprocating aircraft engines. In high blower, the supercharger's impeller is driven through a higher gear ratio, spinning faster relative to the crankshaft to produce greater manifold pressure at high altitude where the air is thin.