What is "optical activity"

optical activity \optical activity\ n. (Chem.) the ability of a chemical compound to rotate the plane of plane-polarized light. This is found only in chemicals whose molecular structure does not have a plane of symmetry, and is common in biochemical compounds. -- optically active adj.

n. 1 (context physics English) a property caused by asymmetrical molecular or crystal structure that enables a compound or crystal to rotate the plane of incident polarized light 2 (context chemistry English) A measure of the amount of optical rotation produced by a standard amount of a substance