A biphosphate is any of the following (due to fluctuations in chemical nomenclature over the centuries):

• One of the two phosphate ions which can be singular to 1 metal ion
  • Monohydrogen phosphate, commonly known as hydrogenphosphate, also known as biphosphate(2-).
  • Dihydrogen phosphate, also known as biphosphate(1-).
• Any salt of phosphoric acid in which only one of the hydrogen atoms has been replaced by a metal ion
  • Calcium biphosphate is monocalcium phosphate
  • Potassium biphosphate is monopotassium phosphate
  • Magnesium biphosphate is monomagnesium phosphate
  • Sodium biphosphate is monosodium phosphate
• Any diphosphate, which may be:
  • Any pyrophosphate
    • Any simple pyrophosphate salt (which have no hydrogen atoms)
      • Calcium pyrophosphate
      • Tetrasodium pyrophosphate
      • Zinc pyrophosphate
    • Any organic pyrophosphate or any organic molecule with two phosphate groups
      • Adenosine diphosphate
        • Deoxyadenosine diphosphate
      • Cytidine diphosphate
        • Deoxycytidine diphosphate
      • Guanosine diphosphate
        • Deoxyguanosine diphosphate
      • Thiamine pyrophosphate
      • Thymidine diphosphate
      • Uridine diphosphate
  • Any salt or ester with two phosphate groups
    • Hexestrol diphosphate