Conjugate acid
A conjugate acid, within the Brønsted–Lowry acid–base theory, is a species formed by the reception of a proton (H) by a base—in other words, it is a base with a hydrogen ion added to it. On the other hand, a conjugate base is merely what is left after an acid has donated a proton in a chemical reaction. Hence, a conjugate base is a species formed by the removal of a proton from an acid.