Definition
Power required (PR) is the amount of engine power an airplane must produce to maintain steady, level flight at a given airspeed and configuration. It equals the drag on the airplane multiplied by the true airspeed, and it varies with speed: high at very slow speeds (because of induced drag), lowest near the airplane's best L/D speed, and rising again at higher speeds (because of parasite drag).
Plain English
The power the engine has to put out just to keep the airplane flying level at a chosen speed. Fly slower or faster than the most efficient speed, and you need more power to hold altitude.
Context Anchor
Seen on climb-performance diagrams, especially where power required is compared with power available to explain rate of climb.
Derivation
Power comes from older words meaning ability or capacity. Required comes from a word meaning needed or asked for. Together, power required means the amount of power needed for a specific flight condition.
Why Pilots Care
It sets the upper limit on climb performance and identifies the airspeeds for best rate and angle of climb.
Grounding Statement
At each airspeed, the airplane has a certain power cost just to keep flying; climb is possible only when the airplane can produce more than that cost.
Intuition Check
Power required does not mean full power or recommended power. It means the minimum power needed for the airplane to maintain that speed and condition.
Example Sentence 1
At the bottom of the power-required curve, the airplane is flying at the speed where the engine has to work least to maintain altitude.
Example Sentence 2
The pilot compared power available to power required to decide whether a climb was possible at the current weight.