Refraction is the bending of light rays when they pass from one medium to another, such as from air to water. This phenomenon occurs because the speed of light changes depending on the medium it is travelling through. When light passes from a less dense medium to a more dense medium, it bends towards the normal line. Conversely, when light passes from a more dense medium to a less dense medium, it bends away from the normal line. Refraction is an important concept in optics and is used in many everyday applications, such as eyeglasses, cameras, and telescopes.