Examples of parallelograms include rectangles, squares and rhombuses. Algebra.com defines a parallelogram as a quadrilateral, or polygon with four sides that are straight, with opposite sides that run parallel to each other.
Not all quadrilaterals meet the criteria for parallelograms. The shape of a kite and some types of trapezoids are not parallelograms. Opposite sides of a parallelogram must be equal in size; the figure?s opposite angles are equal, and its diagonals cut each other in half. Every parallelogram has two pairs of parallel sides. A square is a unique type of parallelogram; its four sides are equal in length, and each angle is 90 degrees.