Definition
Airfoils are shaped surfaces — such as wings, propeller blades, and control surfaces — designed to produce a useful aerodynamic force (primarily lift) as air flows around them. Their cross-sectional shape, with a curved upper surface and flatter lower surface, causes air to flow at different speeds and pressures above and below, generating lift when the airfoil moves through the air at a suitable angle.
Plain English
Airfoils are the specially shaped parts of an airplane — like the wings and propeller blades — that create lift when air flows over them. Their curved shape is what lets the airplane fly.
Context Anchor
Seen in discussions of how wings, tail surfaces, and propellers work as the airplane moves through the air.
Derivation
From 'air' plus 'foil,' an old word for a thin sheet or leaf-like shape (from the Latin 'folium,' meaning leaf). So an airfoil is literally a 'leaf-shaped object designed to work in the air.' That image fits — a wing's cross-section really does look like a thin, curved leaf.
Why Pilots Care
Almost every flying surface on the airplane is an airfoil — wings, propeller blades, horizontal stabilizer, rudder, and ailerons. Understanding how airfoils produce lift is the foundation for understanding stalls, angle of attack, performance, and control.
Intuition Check
Do not think of an airfoil as only the main wing. In aviation, propeller blades and tail surfaces can also be airfoils because they are shaped to work with moving air.
Example Sentence 1
The wings and propeller blades are both airfoils, each shaped to produce lift as air flows across them.
Example Sentence 2
Propeller blades function as rotating airfoils that turn engine power into forward thrust.