In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid.  It most commonly means orthophosphate, a derivative of orthophosphoric acid,  phosphoric acid .
The phosphate or orthophosphate ion  is derived from phosphoric acid by the removal of three protons .  Removal of one proton gives the dihydrogen phosphate ion  while removal of two protons gives the hydrogen phosphate ion . These names are also used for salts of those anions, such as ammonium dihydrogen phosphate and trisodium phosphate.
In organic chemistry, phosphate or orthophosphate is an organophosphate, an ester of orthophosphoric acid of the form  where one or more hydrogen atoms are replaced by organic groups. An example is trimethyl phosphate, .  The term also refers to the trivalent functional group  in such esters. Phosphates may contain sulfur in place of one or more oxygen atoms (thiophosphates and organothiophosphates).
Orthophosphates are especially important among the various phosphates because of their key roles in biochemistry, biogeochemistry, and ecology, and their economic importance for agriculture and industry.  The addition and removal of phosphate groups (phosphorylation and dephosphorylation) are key steps in cell metabolism.
Orthophosphates can condense to form pyrophosphates.