Plain English Meaning

It's the steepest angle the wing can meet the oncoming air before it stops flying. Push past this angle and the wing stalls — every time, no matter how fast you are going.

Full Definition

The angle of attack at which a wing produces its maximum coefficient of lift. Beyond this angle, airflow over the upper surface of the wing separates and the wing stalls, causing a sharp loss of lift regardless of airspeed, weight, or attitude. The CL-MAX critical AOA is a fixed property of the wing's shape and is the same every time, in every flight condition.

Context Anchor

Seen in lift and stall discussions, especially in that show lift increasing with angle of attack up to a peak and then dropping .