Meaning of angle of deviation

an'gle of devia'tion

Pronunciation: [key]
— Optics. Optics.
  1. the angle equal to the difference between the angle of incidence and the angle of refraction of a ray of light passing through the surface between one medium and another of different refractive index. Also called
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.