Acids in which an acidic –OH group has been replaced by an –OOH group, e.g. CH3C(=O)OOH peroxyacetic acid, PhS(=O)2OOH benzeneperoxysulfonic acid.
Source: PAC, 1995, 67, 1307. (Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)) on page 1356 [Terms] [Paper]