Refraction of light is the bending of light as it passes through a medium with a different refractive index. The refractive index is a measure of how much a medium bends light and is determined by the density and composition of the medium.
When light enters a medium with a higher refractive index, it slows down and bends towards the normal (an imaginary line perpendicular to the surface of the medium). When light enters a medium with a lower refractive index, it speeds up and bends away from the normal.
This phenomenon is the reason why objects appear distorted or displaced when viewed through a curved surface or a medium with a different refractive index, such as glass or water.
Refraction of light is also responsible for the formation of optical illusions like mirages, the apparent height of the sun above the horizon and the twinkling of stars.
Refraction of light is also used in many optical instruments such as lenses, prisms, and cameras, to manipulate the light and form an image.