Plain English Meaning
The angle at which the wing meets the oncoming air. The steeper this angle, the more the wing 'bites' into the air — up to a point. Past that point, the airflow breaks away from the wing and lift collapses.
Full Definition
The acute angle formed between the chord line of an airfoil and the relative wind — the direction of the airflow meeting the wing. Angle of attack determines how much lift the wing produces at a given airspeed, and exceeding the critical angle of attack causes the wing to stall regardless of airspeed or aircraft attitude.
Context Anchor
Seen in discussions of lift, slow flight, stalls, takeoff and landing, turns, and .