Plain English Meaning

The speed at which the airplane needs the smallest throttle setting to keep flying level. Fly slower than this and you need more power; fly faster than this and you also need more power.

Full 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 overcome the increased induced drag of high angles of attack; above it, more power is needed to overcome the increased parasite drag of higher speeds.

Context Anchor

Seen in discussions of slow flight, airplane attitude, and how pitch and power affect altitude control.