[b]Parallelograms[/b] are [b]quadrilaterals[/b] whose opposite sides are [u]parallel[/u]. There opposite angles are congruent.[br]A [b]rhombus[/b] is a special parallelogram with all four sides congruent. [br]When all angles of a [b]rhombus[/b] are 90°, it is a [b]square[/b].[br]When all angles are 90° and opposite sides are congruent, it is a [b]rectangle[/b].[br]If you want to work with squares or rectangles, click Angle until you get a 90° angle.

Hence, parallelograms may have multiple names depending upon the values of their angles and/or sides.