optical density [obsolete]

https://doi.org/10.1351/goldbook.O04306
Synonymous with absorbance. The use of the term optical density is discouraged.
Source:
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2257 (https://doi.org/10.1351/pac199668122223)