A chemical compound, with a sour taste, that releases hydrogen ions when dissolved in water.

The strength of the acid depends upon the concentration of hydrogen ions. Acids react with bases, forming salts. Acids have a pH less than 7. Acids can be organic – such as critic, tartaric, tannic, oleic and acetic – and inorganic or mineral – such as sulphuric, hydrochloric, nitric, and phosphoric.