Plain English Meaning
A panel on the back edge of the wing, close to the body of the airplane, that the pilot lowers to help the airplane fly slower and come down more steeply during takeoff and landing.
Full Definition
A movable hinged surface on the trailing edge of the wing, near the fuselage, that can be extended downward to increase lift and drag at lower airspeeds. Flaps are typically used during takeoff and landing to allow the aircraft to fly safely at slower speeds and to descend at a steeper angle without gaining excess airspeed.