Carbonate is a compound ion with a charge of -2 and an elemental formula of CO32-. An aqueous solution of carbon dioxide contains a minute amount of H2CO3, called carbonic acid, which dissociates to form hydrogen ions and carbonate ions. It would be a fairly strong acid if carbonic acid existed in pure form, but the equilibrium favors carbon dioxide and so such solutions are fairly weak. In biological systems the enzyme carbonic anyhdrase catalyzes this interconversion between carbon dioxide and carbonate ions.
Carbonate-containing salts are industrially and minerologically ubiquitous. The term "carbonate" is also commonly used to refer to one of these salts.
The term is also used as a verb, to describe the process of raising carbonate and bicarbonate concentrations in water, see also carbonated water, either by the introduction under pressure of carbon dioxide gas into the water, or by dissoving carbonate or bicarbonate salts into the water.