Description: Sal classifies quadrilaterals by their properties (such as parallel sides). Created by Sal Khan. A parallelogram is a blank with two sets of parallel lines. And a parallelogram is definitely a quadrilateral. A rhombus is a special case of a parallelogram where not only do you have to sets of parallel lines as your sides, two sets of parallel sides, but all of the sides are the same length in a rhombus.*Teacher Advisor is 100% free.