Definition
Hinged, movable surfaces on the trailing edge of the wing, near the fuselage, that can be lowered (extended) to increase the wing's lift and drag at slower airspeeds. Flaps allow the airplane to fly safely at lower speeds, which is useful for takeoff and especially for landing, where they enable a steeper descent path and a slower touchdown.
Plain English
Panels on the back edge of each wing that the pilot can lower to help the airplane fly slower and come down more steeply for landing without stalling.
Context Anchor
You will see flaps on the cockpit flap control, on landing and after-landing checklists, and in procedures that tell you when to extend or retract them.
Derivation
From the everyday word 'flap,' meaning something hinged that swings up or down. The aviation term keeps the same idea — a panel that swings down from the wing.
Why Pilots Care
Flap setting changes how the airplane climbs, descends, and handles. Wrong flap selection on takeoff or landing — or retracting them at the wrong moment — can cause loss of lift, a hard landing, or a stall close to the ground.
Analogy
Flaps are a little like changing the shape of your hand when you hold it out of a car window. A small change in shape can make the air push on it differently.
Intuition Check
Do not think of flaps as loose parts that simply flap in the wind. In an airplane, flaps are controlled wing surfaces that the pilot sets to specific positions.
Example Sentence 1
After clearing the runway, the pilot retracted the flaps as part of the after-landing checklist.
Example Sentence 2
On final approach the pilot extended the flaps to 20 degrees so the airplane could maintain altitude at a slower speed.