Definition
The minimum airspeed at which an airplane, in a given configuration and at a given weight and load factor, can maintain level flight without exceeding the critical angle of attack. Below this speed, the wing can no longer produce enough lift to support the airplane and a stall occurs.
Plain English
The slowest speed at which the wings can still hold the airplane up. Go any slower and the wings stop working as wings, and the airplane stalls.
Context Anchor
Seen in stall training, takeoff and landing planning, and airspeed indicator markings for clean and landing-configuration stall speeds.
Derivation
Stall comes from an old word meaning to come to a standstill or stop working. The wing hasn't stopped moving, but it has stopped producing usable lift, so it stalls in the working sense of the word.
Why Pilots Care
Knowing stalling speed allows pilots to maintain safe margins above it during takeoff, landing, and maneuvering to prevent an unintended stall.
Intuition Check
Do not read this as the engine stalling or the airplane stopping in the air. Stalling speed is about the wing reaching the stall angle for the airplane’s current condition.
Example Sentence 1
In a 60-degree level turn, the load factor doubles the effective weight, so stalling speed increases by about 40 percent over the wings-level value.
Example Sentence 2
Higher weight from extra fuel raised the airplane’s stalling speed for the return flight.