A parallelogram is a four-sided plane figure that has two sets of opposing, parallel sides.
Every parallelogram is a polygon, and more specifically a quadrilateral.
Special cases of a parallelogram are rectangles, in which the two sets of opposing, parallel sides are perpendicular to each other, and squares, rectangles in which all four sides are equal.
The 3d equivalent of a prallelogram is a parallelepiped.
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