Plain English Meaning

The air stops hugging the surface and breaks away into a messy, churning flow. When that happens, the wing or tail can no longer do its job properly.

Full Definition

A condition in which the smooth flow of air over a wing or other surface breaks away from that surface instead of following its contour. Once the airflow separates, it becomes turbulent and disorganized, and the surface loses much of the lift or control authority it would normally produce.

Context Anchor

Seen in discussions of stalls, high nose-up attitudes, and T-tail airplanes, where disturbed air from the wing can affect the tail.

Derivation

‘Separated’ comes from the Latin separare, meaning ‘to set apart.’ The airflow literally sets itself apart from the surface it had been following.