Phosphoric acid (also known as orthophosphoric acid or phosphoric(V) acid) is a mineral (inorganic) acid having the chemical formula H3PO4. Orthophosphoric acid molecules can combine with themselves to form a variety of compounds which are also referred to as phosphoric acids, but in a more general way. Orthophosphoric acid refers to phosphoric acid, which is the IUPAC name for this compound. The prefix ortho is used to distinguish the acid from related phosphoric acids, called polyphosphoric acids. Orthophosphoric acid is a non-toxic acid, which, when pure, is a solid at room temperature and pressure.

The conjugate base of phosphoric acid is the dihydrogen phosphate ion, H
2PO−
4, which in turn has a conjugate base of hydrogen phosphate, HPO2−
4, which has a conjugate base of phosphate, PO3−
4.

Source: Wikipedia.com