Plain English Meaning

Tiny moving flaps on the outside of the aircraft that swing to point into the oncoming air. By measuring how they rotate, the aircraft can tell what angle the wing is meeting the air at.

Full Definition

Small, thin, flat or slightly curved blades mounted on the exterior of an aircraft that pivot freely in the airflow. In angle of attack indicators, vanes align themselves with the relative wind and mechanically or electrically signal the angle between the wing and that airflow to a cockpit display.

Context Anchor

Seen in angle-of-attack indicator discussions, usually as small sensing pieces mounted where outside airflow can reach them.

Derivation

From the Old English 'fana,' meaning a small or banner. The original idea — a flat that swings to show — carries straight to the use, where the vane points into the relative wind.