angle of attack

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The acute angle between the chord of an airfoil and a line representing the undisturbed relative airflow.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Used other than as an idiom: see angle,‎ attack.
• noun aeronautics The angle between the chord line of an airfoil and the airflow over it; one of the determiners of the amount of lift produced by an airfoil.
• noun nautical The angle between a mid-sail and the direction of the wind.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the acute angle between the direction of the undisturbed relative wind and the chord of an airfoil