This document discusses the concept of refraction of light. It defines refraction as the change in direction of light when it passes from one medium to another. It explains that when light travels from a less dense to a more dense medium, it bends toward the normal, and when traveling from more dense to less dense, it bends away from the normal. It also introduces the laws of refraction, refractive index, angle of incidence and refraction, total internal reflection, and optical density. Total internal reflection occurs when the angle of incidence is greater than the critical angle and the light ray travels from a denser to a less dense medium.