word best describes a parallelogram with diagonals that are congruent and perpendicular?

Answer: Square

Step-by-step explanation:

A parallelogram is a closed polygon having 4 sides, such that

Opposite sides are parallel. Opposite sides are congruent. Opposite angles are congruent. Diagonals bisects each other.

Also,

When diagonals of a parallelogram are congruent and perpendicular, then it is a square. If diagonals are just perpendicular, then we call it a rhombus. If diagonals are just congruent, then we call it a rectangle.

Hence, the word best describes a parallelogram with diagonals that are congruent and perpendicular would be " Square".