The bending or changing direction of a light ray as it passes through material is...

Refraction is the bending of light as it passes from one medium to another with a different density, such as from air to glass. This change in direction occurs because the speed of light changes in different media.

CTS Technology Specialist Reference

In AV, understanding refraction is essential for systems involving optics, such as projectors and lenses, where light paths affect image quality and focus.