is: the process in which the direction of a light ray changes either at the boundary between two transparent materials of different refractive index or through a region of varying refractive index. [P6.2]
more generally is: the process by which a wave's direction of propagation is changed as it travels through varying materials. The bending is a direct consequence of the different speeds of the wave in the different materials - dispersion. [P5.7, P6.1]
See law of refraction.
Copyright 1997, The Open University