Plain English Meaning
The wing is meeting the oncoming air at a steep angle. The airplane is flying close to the angle where the wing stops producing lift, so it is operating near its limit.
Full Definition
A flight condition in which the angle between the wing's chord line and the relative wind is large, approaching the critical angle at which the wing will stall. High AOA is associated with slow flight, steep climbs, and the landing flare, where the wing is producing lift close to its maximum coefficient.
Context Anchor
Seen during slow flight, short-field approaches, , and any of .