Definition
In aerodynamics, stalling is the condition in which a wing's angle of attack exceeds the critical angle, causing the smooth airflow over the upper surface to separate and a sudden loss of lift to occur. A stall is a function of angle of attack, not airspeed, and can happen at any airspeed, any altitude, and any power setting.
Plain English
Stalling is what happens when the wing is tilted too steeply into the oncoming air. The air can no longer flow smoothly over the top of the wing, so the wing stops producing enough lift to hold the airplane up.
Context Anchor
Seen in aerodynamics and thrust discussions, especially when describing how wings and propeller blades behave when their angle to the airflow becomes too high.
Derivation
From the older mechanical sense of 'stall' meaning to come to a standstill or stop working. In aviation it was borrowed to describe the wing 'quitting' on the pilot — not the engine stopping, but the lift stopping.
Why Pilots Care
A stall produces an immediate loss of lift and control authority; prompt recognition and recovery are required for safe flight.
Grounding Statement
Picture a wing or propeller blade tilted so steeply into the air that the air can no longer flow smoothly over it.
Intuition Check
Stalling does not mean the engine has quit, and it does not simply mean the airplane is moving slowly. In aviation, stalling means the airflow over a wing or propeller blade has broken down because the angle to the airflow is too great.
Example Sentence 1
The instructor demonstrated stalling the airplane in a clean configuration so the student could feel the buffet and recognise the warning signs.
Example Sentence 2
During slow-flight practice the airplane approached the stall at a high angle of attack.