In a chemical reaction involving chiral reactants and products, the ratio of the optical purity of the product to that of the precursor, reactant or catalyst. This should not be confused with enantiomeric excess. The optical yield is in no way related to the chemical yield of the reaction.
See: stereoselectivity
Sources:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1146 (https://doi.org/10.1351/pac199466051077)
PAC, 1996, 68, 2193. 'Basic terminology of stereochemistry (IUPAC Recommendations 1996)' on page 2212 (https://doi.org/10.1351/pac199668122193)