Simplify the following text for a Grade 8 native English-speaking person.
Original: Not every parallelogram is a rhombus , though any parallelogram with perpendicular diagonals ( the second property ) is a rhombus .
Simplified: A rhombus is a parallelogram ( four-sided polygon where opposite sides are parallel ) with all sides equal in length . A rhombus with all angles equal is called a square .