Definition
A hinged or movable secondary control surface attached to the trailing edge of an aircraft wing, used to increase lift and drag at lower airspeeds. Flaps are extended (lowered) for takeoff and landing to allow the aircraft to fly safely at slower speeds and to steepen the descent path, and retracted in cruise flight.
Plain English
A movable panel on the back edge of the wing that the pilot lowers to help the aircraft fly slowly without stalling. Lowering the flaps changes the shape of the wing so it can produce more lift at slower speeds, which is useful for takeoff and especially for landing.
Context Anchor
You will see flaps discussed in preflight checks, takeoff and landing procedures, cockpit controls, and aircraft maintenance descriptions of wing systems.
Derivation
From the Old English 'flappe', meaning something that hangs loose and moves. The name describes what the surface does: it hangs down from the trailing edge of the wing when extended.
Why Pilots Care
Enables safe flight at speeds below clean stall speed and shortens takeoff and landing distances; misuse can cause excessive drag, structural overload, or asymmetric lift.
Intuition Check
Do not think of a flap as any loose panel or cover. In this context, a flap is a specific movable wing control surface used to change how the wing performs.
Example Sentence 1
On final approach, the pilot lowered full flaps to slow the aircraft and steepen the descent toward the runway.
Example Sentence 2
On final approach the instructor called for full flaps to allow a slower touchdown speed.