Description: Learn about the properties of quadrilaterals, parallelograms, trapezoids, rhombuses, rectangles, and squares. Created by Sal Khan and Monterey Institute for Technology and Education. And this is definitely a closed shape that has four sides. A parallelogram is a quadrilateral that has two pairs of parallel sides, where in each pair they're opposite sides. And in this case, if you look at this side over here, it forms a 90-degree angle with this line.*Teacher Advisor is 100% free.