Definition
The maximum horizontal distance an airplane can travel through the air without engine power, achieved by flying at the airspeed that produces the highest lift-to-drag ratio. This airspeed is published in the Pilot's Operating Handbook and varies with aircraft weight.
Plain English
The farthest the airplane can glide forward when the engine quits, if you fly it at exactly the right airspeed. Too fast or too slow and you don't get as far.
Context Anchor
Used during power-off descents, especially when deciding whether a landing area is within reach after an engine failure.
Derivation
Glide comes from an old word meaning to move smoothly. In aviation, it helps to think of the airplane still moving forward smoothly through the air while it is coming down, rather than simply dropping.
Why Pilots Care
Selecting and holding this airspeed after an engine failure gives the greatest chance of reaching a suitable landing area that would otherwise be unreachable.
Grounding Statement
If the engine stops at altitude, best glide distance is the practical limit of how far ahead you can expect the airplane to travel before reaching the ground.
Intuition Check
Best does not mean slowest, steepest, or safest in every situation here. It means the glide condition that gives the most forward distance from the height you have.
Example Sentence 1
After the engine lost power, the pilot pitched for best glide airspeed to reach maximum best glide distance toward the nearest field.
Example Sentence 2
A tailwind increases best glide distance while a headwind reduces it, so the pilot adjusted the target airspeed slightly.