The normal line is a line at a right angle (90 degrees) to the surface of an object

To draw a normal line to the mirror, you must draw a line at 90 degrees to the surface of the mirror.

Why do we always refer to the angle with the normal line in physics? - Quora

Laws of Reflection - Definition, Types, Formula, Uses, & FAQs

Right Angles, Definition and Examples

Azimuth - Wikipedia

Right angle

Angle of Reflection Definition, Types & Formula - Lesson

Images formed by an object placed between two plane mirros whose reflecting surfaces an angle of 90^{circ} with one another lie on a

Why, in optics, do we measure the angle of incidence between the normal line and the light rays? - Quora

Measurement, Shape and Space - Mr. Grant's Class

PF1.2 Forces on Slopes

Aligning Object to Surface using CFrame:fromMatrix() - Community Tutorials - Developer Forum

Optics, History, Applications, & Facts