An inositol phospholipid.

Phosphatidylinositol (abbreviated PtdIns, or PI) is a minor phospholipid component in the cytosolic side of eukaryotic cell membranes. Phosphatidylinositol is a class of phospholipid, which is made up of glycerol, fatty acid and the base is replaced by a hexahydric alcohol namely inositol. This hexahydric alcohol exists as its stereoisomer - myo-inositol.