Definition
A hinged, movable surface attached to the trailing edge of the wing, inboard of the ailerons, that can be deflected downward to increase lift and drag. Flaps are extended in stages to allow slower flight speeds for takeoff and landing while maintaining controlled airflow over the wing.
Plain English
A panel on the back edge of the wing that the pilot lowers to make the wing produce more lift at slower speeds. Lowering flaps also adds drag, which helps the airplane slow down and descend more steeply.
Context Anchor
You will encounter flaps during preflight checks, takeoff setup, approach planning, landing, and go-around procedures.
Derivation
From Old English 'flappe', meaning a broad, loose piece that hangs and can be moved. The aviation use kept the everyday sense of a hinged panel that swings down out of its stowed position.
Why Pilots Care
Flaps let the aircraft maintain lift at lower speeds, shortening takeoff and landing distances while improving control near the ground.
Intuition Check
Do not think of a flap as something loose that flutters in the wind. On an airplane, a flap is a controlled wing surface that the pilot sets to a specific position.
Example Sentence 1
On final approach, the pilot extended full flaps to slow the airplane and steepen the descent toward the runway.
Example Sentence 2
On takeoff the pilot set the flaps to ten degrees to improve climb performance.