angle of reflection

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. The angle formed by a reflected ray and a perpendicular to the surface at the point of reflection.

Wiktionary

1. n. optics The angle between the perpendicular and a ray reflected from a surface

GNU Webster's 1913

1. n. the angle which anything, as a ray of light, on leaving a reflecting surface, makes with the perpendicular to the surface.

WordNet 3.0

1. n. the angle between a reflected ray and a line perpendicular to the reflecting surface at the point of incidence