Aviation term for the hinged surface on the trailing edge of an aircraft wing, used to increase lift or drag.
The pilot lowered the flaps before landing.
seal flap (envelope)
Refers to the foldable part of an envelope used to seal it; also used for similar flaps on packaging.
I sealed the envelope flap with glue.
The flaps were lowered before landing.
I sealed the envelope's flap firmly.
After takeoff, the flaps were raised.