Definition
The airspeed at which an airplane in level flight requires the least amount of engine power to maintain altitude. Below this speed, more power is needed to stay level because induced drag rises sharply; above this speed, more power is needed because parasite drag rises. It marks the bottom of the power-required curve and lies on the slow side of the airspeed range, in the region of reversed command.
Plain English
The speed at which the airplane needs the smallest throttle setting to hold altitude. Fly slower or faster and you'll need more power to stay level.
Context Anchor
Seen when learning how elevator position changes airspeed and how much power is needed to hold altitude.
Derivation
Minimum comes from a Latin word meaning smallest. Here it points to the airspeed where the required power is at its smallest amount, not to the slowest airspeed the airplane can fly.
Why Pilots Care
Flying at this speed maximizes endurance by using the least fuel per unit of time when remaining aloft is the priority.
Grounding Statement
Picture level flight: as the airplane slows from cruise, the power needed drops to a low point, then starts rising again as the airplane gets even slower.
Intuition Check
Minimum power airspeed does not mean the minimum safe airspeed or the slowest possible airspeed. It means the airspeed where the airplane needs the least power to keep flying level.
Example Sentence 1
As the airplane decelerated below minimum power airspeed, the pilot had to add throttle just to hold altitude.
Example Sentence 2
In training, the student maintained minimum power airspeed to feel how little throttle was needed once the airplane was trimmed for level flight.