What is a Biconditional statement?

Answer 1

something in which the coditional statement itself is true and its converse is true

Answer 2

A biconditional usually includes the phrase "if and only if". It means the statement should be true as two separate if / then statements. For example "A triangle is equilateral if and only if all its angles are congruent" could be written as two sentences: "If a triangle is equiltaeral, then all its angles are congruent" and "If all its angles are congruent, then a triangle is equilateral." Virtually all definitions and a lot of theorems are biconditionals.