Derivatives of glycerol in which one hydroxy group, commonly but not necessarily primary, is esterified with phosphoric acid and the other two are esterified with fatty acids.
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See: fatty acids, lecithins, phosphoglycerides, phospholipids
Sources:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1357 (https://doi.org/10.1351/pac199567081307)
White Book, 2nd ed., p. 184 (https://iupac.qmul.ac.uk/bibliog/white.html)