any of various water-soluble compounds having a sour taste and capable of turning litmus red and reacting with a base to form a salt

a crystalline tetrabasic acid (H4P2O6)

a clear or yellow monobasic acid (H3PO2)

a series of oxyacids of phosphorus

any acid of iodine that contains oxygen

an acid used in fertilizers and soaps: H3PO4