The answer is biconditional statement.
A biconditional statement is a statement that can be rewritten as a conditional or a converse. It is deemed true if the conditional and the converse statement is true. You can tell whether the statement is biconditional with the words, "if and only if."
Here is an example:
A polygon is a quadrilateral if and only if it has four sides.
A polygon has four sides, if and only if, it is a quadrilateral.
Since both statements are true, then this is a true biconditional statement.
