Illustrated Glossary of Organic Chemistry

Phosphate: An anion consisting of phosphorous bonded to four oxygen atoms, or a molecule containing a phosphate group.

Phosphate Ions

Monophosphate ion
Diphosphate ion
(Pyrophosphate ion)
Triphosphate ion

Example Molecules Containing a Phosphate Group

Trimethyl phosphate, an organophosphate (phosphate ester).   
5'-Adenylic acid, is a nucleotide and a phosphate ester.