Plain English Meaning
When the wind blowing against the airplane suddenly weakens or reverses, the airplane loses airspeed and starts to sink. This is a dangerous moment, especially close to the ground.
Full Definition
The sudden loss of indicated airspeed and lift that occurs when an aircraft flies out of a headwind into calmer air or a tailwind, typically during a microburst or wind shear encounter. As the headwind component decreases, the aircraft's airspeed drops, lift reduces, and the airplane tends to sink below the intended flight path.
Context Anchor
Seen in low-level wind shear discussions, especially during , , and close to the ground.