A quadrilateral is a polygon with four sides.
A trapezoid is a quadrilateral that has at least one pair of parallel sides.
A quadrilateral with no parallel sides is called a common quadrilateral.
A parallelogram is a quadrilateral with two pairs of parallel sides and two pairs of equal-length sides.
A rectangle is a quadrilateral with opposite sides that are parallel and equal in length and all four angles are right angles.
Parallelograms that do not meet the definition of a rectangle are called common parallelograms.
A rhombus is a quadrilateral with equal sides, two pairs of which are parallel.
A square is a quadrilateral with equal sides, two pairs of which are parallel, and all right angles.
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