In short
The angle of reflection is the angle between a reflected ray of light and the normal, the line drawn at right angles to the surface at the point where the ray hits it.
Light bounces off a mirror and leaves at the same angle at which it arrived. Both angles are measured from the normal, never from the surface itself. The law of reflection says that the angle of reflection equals the angle of incidence, and that the incident ray, the reflected ray and the normal all lie in one plane.
A ray strikes a plane mirror so that it makes with the normal. The reflected ray also makes with the normal, so the angle between the incident and reflected rays is .
Also searched as: angle of the reflected ray, law of reflection.