- 1a: A salt or ester of a phosphoric acid; b: the trivalent anion PO43- derived from phosphoric acid (H3PO4).
2: An organic compound of phosphoric acid in which the acid group is bound to nitrogen or a carboxyl group in a way that permits useful energy to be released (as in metabolism).
Definition from: Merriam-Webster's Medical Dictionary by Merriam-Webster Inc.
Related discussion in the Handbook
See also Understanding Medical Terminology.