Compounds consisting of two acyl groups bonded to the same oxygen atom acyl-O-acyl. Symmetric and mixed anhydrides have identical and different acyl groups, respectively. E.g.
acetic benzenesulfonic anhydride,
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1311 (https://doi.org/10.1351/pac199567081307)