Plain English Meaning

How much work the engine is producing per unit of time. More power means the engine is doing more work, which the propeller turns into thrust to push the airplane forward, climb, or accelerate.

Full Definition

In aviation, power is the rate at which an engine does work, typically measured in horsepower. In a piston aircraft, power output is controlled primarily by the throttle (which sets manifold pressure) and, in constant-speed propeller installations, the propeller control (which sets engine RPM). Power determines how much thrust the propeller can produce and, together with pitch attitude, how the airplane , cruises, or descends.