Definition:Logical Complement/Complementary Pair

Definition
For any propositional formula $\mathbf A$, the set $\left\{{\mathbf A, \neg \mathbf A}\right\}$ is called a complementary pair of formulas.

Also known as
In case $\mathbf A$ is an atom, $\left\{{\mathbf A, \neg \mathbf A}\right\}$ is called a complementary pair of literals for $\mathbf A$.