Wiktionary
phosphatidic acid
n. (context chemistry English) any derivative of glycerol in which one hydroxyl is esterified with phosphoric acid and the other two are esterified with fatty acids
Wikipedia
Phosphatidic acid
Phosphatidic acids (PAs) are the acid forms of phosphatidates, a part of common phospholipids, major constituents of cell membranes. Phosphatidic acids are the simplest diacyl- glycerophospholipids.