angle of attack

Short definition from Wiktionary

Noun

1. 1
   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.
2. 2
   The angle between a mid-sail and the direction of the wind.
3. 3
   The angle between the plane of rotation of a wheel and the outer rail in the track curve.
4. 4
   Used other than figuratively or idiomatically: see angle, attack.