The property of nonisotropic media, such as crystals, whereby a single incident beam of light traverses the medium as two beams, each plane-polarized, the planes being at right angles to each other. (Cline et al., Dictionary of Visual Science, 4th ed)

Synonyms: Double Refraction, Birefringences, Refraction, Double, Double Refractions, Refractions, Double, Birefraction, Birefractions, Birefringence