Refraction is the bending of light (or other waves) as it passes from one medium to another with a different density. This phenomenon occurs due to the change in the speed of light as it moves between different substances, such as air, water, or glass. When light enters a denser medium (like from air to water), it slows down and bends toward the normal (an imaginary line perpendicular to the surface at the point of incidence).
New to topics? Read the docs here!