The angle of incidence is the angle between the incident ray and the normal.
Step-by-step explanation:
In attached diagram, a light ray approaching the mirror is known as an incident ray (I) whereas the light beam coming out of the mirror is called the reflected ray (R). At the intersection where the beam meets the mirror, you can draw a line perpendicular to the mirror surface.
This line is called as the normal (N) line. Normal divides the angle between the incident and the reflected rays into two equal angle. The angles between the incident and normal beam is called the incidence angle (
). The angle between the reflected beam and the normal one is called the reflection angle(
).