Plain English Meaning
The instant the airplane stops rolling on the ground and starts flying.
Full Definition
The moment during the takeoff roll when the airplane's wings produce enough lift to overcome its weight and the wheels leave the runway surface, transitioning the aircraft from ground operation to flight.
Context Anchor
Used during takeoff training and takeoff discussions, especially when describing the exact moment the airplane leaves the surface.
Derivation
A straightforward compound: the airplane is 'lifted off' the ground by the lift its wings generate. The hyphenated form is the standard FAA spelling when used as a noun.