When carbon dioxide is dissolved in water carbonic acid, H2CO3, is formed.
Carbonic acid (ancient name acid of air or aerial acid) has the formula H2CO3. It is also a name sometimes given to solutions of carbon dioxide in water, which contain small amounts of H2CO3. The salts of carbonic acids are called bicarbonates (or hydrogencarbonates) and carbonates. It is a weak acid. (wikipedia)