Leading-edge slat

A movable surface at an aircraft wing’s leading edge that extends to form a gap ahead of the wing. The gap helps airflow remain attached at high angles of attack, delaying stall.

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Boundary layer: A thin region of fluid near a surface where viscosity strongly affects the flow. The slat helps control this near-wing flow as the aircraft approaches stall.
Airfoil: A cross-sectional shape designed to produce aerodynamic forces as fluid flows around it. A slat modifies the effective leading-edge shape of an airfoil.
Automatic slat: A slat that extends or retracts in response to aerodynamic forces rather than direct pilot command. Some aircraft use automatic extension as local airflow conditions change.
Leading-edge flap: A hinged leading-edge surface that changes an airfoil’s shape when deployed. It changes leading-edge camber without necessarily creating the slat’s airflow passage.
Flow separation: The detachment of fluid flow from a surface, often causing increased drag and reduced aerodynamic performance. Slats delay the separation that would otherwise limit lift at high angles of attack.
Camber (aerodynamics): The curvature of an airfoil’s mean line between its leading and trailing edges. Extending a slat changes the wing’s effective curvature and lift characteristics.
Fixed slat: A stationary leading-edge surface that leaves a permanent slot ahead of the wing. It provides slat-like stall benefits without a retracting mechanism.
Droop nose: A movable wing leading edge that rotates or lowers to improve low-speed aerodynamic performance. A droop nose reshapes the leading edge rather than opening a slat gap.
Angle of attack: The angle between an airfoil’s reference line and the oncoming airflow. Slats extend the usable range of this angle before stall.
High-lift device: A device that increases an aircraft wing’s lift, especially during takeoff and landing. Slats are leading-edge high-lift devices, often paired with trailing-edge devices.