Obsolescent synonym for stereoisomers with different optical properties. They should be described as diastereoisomers or enantiomers. (Usage strongly discouraged).
Source:
PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2212 (https://doi.org/10.1351/pac199668122193)