intramolecular cyclic esters of hydroxy sulfonic acids, analogous to lactones.
S06131.png
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1370 (https://doi.org/10.1351/pac199567081307)