Brønsted acid

A molecular entity capable of donating a hydron (proton) to a base, (i.e. a 'hydron donor') or the corresponding chemical species. For example: H2O, H3O+, CH3CO2H, H2SO4, HSO4, HCl, CH3OH, NH3 .
See also: conjugate acid–base pair
PAC, 1994, 66, 1077 (Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)) on page 1091