Definition
The angle of attack at which an airfoil's smooth airflow breaks down and lift drops sharply. Beyond this angle, the wing can no longer produce enough lift to support the aircraft, regardless of airspeed or attitude.
Plain English
The steepest tilt the wing can meet the oncoming air at before it stops flying properly. Tilt the wing past this point and it stops producing the lift you need, and the aircraft begins to fall.
Context Anchor
Seen in aerodynamics and icing discussions, especially when explaining how ice on a wing can make an airplane stall sooner than expected.
Derivation
From the older sense of 'stall' meaning to come to a standstill or stop working. Applied to a wing, it describes the moment the wing 'stops working' as a lifting surface. 'Angle' here refers specifically to angle of attack — the angle between the wing and the oncoming air.
Why Pilots Care
Ice buildup lowers the stall angle, so the wing can stall at a lower angle of attack than normal and with less warning.
Grounding Statement
Picture a wing meeting the oncoming air: at a small angle the air flows smoothly, but past the stall angle the air breaks away and lift drops.
Intuition Check
Do not read stall as the airplane stopping or the engine quitting. Here, stall means the wing has reached too great an angle to the oncoming air and can no longer make normal lift.
Example Sentence 1
Ice on the leading edge lowers the stall angle, so the wing can stall at a shallower pitch attitude than normal.
Example Sentence 2
The pilot recognized that the changed stall angle from contamination required a lower angle of attack during the approach.