I think angle of attack is:
The angle between your direction of travel, and where your wings are pointed...When it gets too high, you stall, as the airflow over the wing is disrupted. This is why when you pull a tight turn, even at a high speed, you can still stall - what you've done in this case is made you Angle of Attack to high, disrupting the airflow over your wings, resulting in a loss of lift and thus you stall.
Please correct me if I'm wrong.
<S>
Yossarian