Natural products and related compounds formally derived from isoprene units (see isoprenoids). They contain oxygen in various functional groups. This class is subdivided according to the number of carbon atoms in the same manner as are terpenes. The skeleton of terpenoids may differ from strict additivity of isoprene units by the loss or shift of a fragment, generally a methyl group.
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1371 (https://doi.org/10.1351/pac199567081307)
See also:
White Book, 2nd ed., p. 255 (https://iupac.qmul.ac.uk/bibliog/white.html)