Definition
High-lift devices mounted on the front edge of the wing that extend or droop downward to increase the wing's camber and lift coefficient at low airspeeds, particularly during takeoff and landing. By reshaping the leading edge, they delay the airflow separation that would otherwise cause a stall at higher angles of attack.
Plain English
Movable panels on the front of the wing that fold down to give the wing more curve at slow speeds, so it produces more lift and is harder to stall.
Context Anchor
Seen in airfoil design, aircraft systems descriptions, and checklist items for airplanes equipped with high-lift devices.
Derivation
"Leading edge" simply means the forward edge of the wing — the part that meets the air first. "Flap" comes from the idea of a hinged panel that folds. Together the term describes a hinged panel on the front of the wing, distinguishing it from the more familiar trailing edge flap at the back.
Why Pilots Care
They improve low-speed handling and reduce stall speed during takeoff and landing.
Intuition Check
Do not confuse leading edge flaps with the more familiar flaps on the rear of the wing. Leading edge flaps are on the front of the wing and change how the air first meets the wing.
Example Sentence 1
As the airliner slowed for approach, the leading edge flaps extended a few seconds before the trailing edge flaps reached landing position.
Example Sentence 2
Extending the leading edge flaps allowed the aircraft to climb out at a steeper angle without stalling.