Answer: Square
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".