Plain English Meaning
A strong feeling that the airplane is doing something it isn't — leaning, turning, climbing, or diving — when in fact it isn't. The body is telling the pilot one thing while the instruments show another.
Full Definition
A pilot's false sensation of motion or position in space, caused by conflicting or misleading signals from the inner ear, eyes, and body when visual reference to the horizon is lost. It is a form of spatial disorientation that can persist even when the flight instruments clearly show the actual aircraft attitude.
Context Anchor
Pilots may encounter vertigo when flying from clear visual conditions into cloud, haze, darkness, or any situation where the outside horizon is no longer visible.