Monocyclic compounds containing a metal atom and saturated carbon atoms as ring members, e.g.:
M03864.png
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1349 (https://doi.org/10.1351/pac199567081307)