Plain English Meaning

It's the steady, engine-idle descent flown at the specific speed that lets the airplane travel the farthest possible distance for the height it has available. Fly faster or slower than that speed and the airplane comes down sooner.

Full Definition

A power-off descent flown at the airspeed and pitch attitude that produce the airplane's best lift-to-drag ratio (L/D max), resulting in the greatest distance traveled forward for each foot of altitude lost. The normal glide speed is published in the Pilot's Operating Handbook for the airplane's maximum gross weight and is flown with the propeller in the lowest practical drag setting.

Context Anchor

Seen when practicing glides, power-off descents, , and simulated engine- situations.