Plain English Meaning

The far end of the wing where it stops. Air leaks around this end from below to above, which creates a swirling flow and adds drag.

Full Definition

The outermost end of an airfoil — most commonly the wingtip — where the upper and lower surfaces of the wing come together and the wing terminates laterally. Because higher-pressure air beneath the wing spills around this end into the lower-pressure area above, the airfoil tip is the source of wingtip vortices and contributes to induced drag.

Context Anchor

Seen in discussions of wing shape, wingtip vortices, induced drag, and why a real wing behaves differently from a flat two-dimensional airfoil drawing.

Derivation

‘Airfoil’ is the wing’s shaped surface that produces lift; ‘tip’ is the far end of something. Together, the airfoil tip is simply where that lifting surface ends — and that boundary is where the pressure between top and can finally escape sideways.