While angle of attack varies during flight, angle of incidence is fixed with the design of the aircraft. Airfoils are generally attached to the aircraft at a small angle in relation to its longitudinal axis.
The angle between the direction of propagation of an electromagnetic or acoustic wave ( or ray) incident on a body and the local normal to that body (although this normal may not be well defined, as that for a cloud, e.g.).
May also describe beams of particles in the broadest sense.
Angle of Incidence has been defined 6 different ways in documents like 2014 NAL Thesaurus, 2015 NAL Glossary, Glossary of Terms, and 3 more.