contrapositive
The conditional "if not Q, then not P," which is equivalent to "if P, then Q."
The contrapositive of A → B is ¬B → ¬A. A conditional and its contrapositive are logically equivalent, unlike a conditional and its converse or its inverse.
Examples
The contrapositive of "if it's a dog, it's a mammal" is "if it's not a mammal, it's not a dog."
See also