A loosely defined term for substances of biological origin that are soluble in nonpolar solvents. They consist of saponifiable lipids, such as glycerides (fats and oils) and phospholipids, as well as nonsaponifiable lipids, principally steroids.
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1348 (https://doi.org/10.1351/pac199567081307)
See also:
White Book, 2nd ed., p. 180 (https://iupac.qmul.ac.uk/bibliog/white.html)