What is true of all rhombuses?

-- The rhombus has four sides.

-- All four of its sides are equal in length.

-- Its opposite sides are parallel.

-- The sum of its interior angles is 360 degrees.

-- Its opposite angles are equal.

-- Its diagonals are perpendicular and bisect each other.

A rhombus with all 4 angles equal (at 90°) is called a square (which is a special kind of rectangle in which all 4 sides are of equal length); thus some rhombuses are rectangles (and some rectangles are rhombuses).