The Brønsted acid
BH+ formed on protonation of a base
B is called the conjugate acid of
B, and
B is the conjugate base of
BH+. (The conjugate acid always carries one unit of positive charge more than the base, but the absolute charges of the species are immaterial to the definition.) For example: the Brønsted acid
HCl and its conjugate base
Cl− constitute a conjugate acid–base pair.
Source:
PAC, 1994, 66, 1077. 'Glossary of terms used in physical organic chemistry (IUPAC Recommendations 1994)' on page 1099 (https://doi.org/10.1351/pac199466051077)