Snell's Law relates the angles at which light rays enter and exit different mediums, describing how they refract (bend) due to changes in speed.
Refraction: The bending of light as it passes from one medium to another due to a change in its speed.
Index of Refraction: A measure of how much a material can slow down the speed of light compared to its speed in a vacuum.
Total Internal Reflection: The complete reflection of light at the boundary between two mediums when the angle of incidence is greater than the critical angle.