Definition
Hinged surfaces mounted on the rear (trailing) edge of a wing that can be lowered to increase lift and drag. Pilots extend them during takeoff and landing to allow the aircraft to fly safely at lower speeds and to steepen the descent path on approach.
Plain English
Movable panels on the back edge of the wing that fold down. When you lower them, the wing produces more lift at slow speeds and the airplane can also slow down and descend more steeply, which is useful for takeoff and landing.
Context Anchor
You will see this term in airfoil design, aircraft performance, takeoff and landing procedures, and checklist items that call for a flap setting.
Derivation
Trailing edge means the rear edge of the wing — where the air leaves it — as opposed to the leading edge at the front. Flap comes from an old word meaning something that hangs loose and can be moved up and down, like a flap of cloth. The name describes exactly what these surfaces do: they hang from the back of the wing and move down.
Why Pilots Care
They allow the airplane to generate enough lift at lower speeds for safe takeoffs and landings.
Intuition Check
Do not think of “flaps” as loose pieces hanging from the wing. In aviation, trailing edge flaps are designed movable wing panels that the pilot sets to specific positions.
Example Sentence 1
On final approach, the pilot lowered the trailing edge flaps to the full setting to reduce the landing speed.
Example Sentence 2
With the trailing edge flaps lowered, the airplane could maintain level flight at a lower airspeed during the approach.