A parallelogram is a quadrilateral with each side is parallel to its opposite side. The measure of opposite sides and opposite angles are congruent.The diagonals of a parallelogram bisect each other. But may not be perpendicular.
A rectangle is a kind of parallelogram is a quadrilateral with each side is parallel to its opposite side. Its each interior angle is a right angle.The diagonals of a parallelogram bisect each other but may not be perpendicular.
A square and a rhombus is also a kind of quadrilateral where each side is parallel to its opposite side but the diagonal are perpendicular to each other..