A rhombus is a parallelogram. Remember that opposite sides of a parallelogram are always congruent. A rhombus also has two pairs of opposite congruent angles. Angles that are across from each other are congruent.
A square is a type of rectangle. Remember, a square is a type of quadrilateral that has all sides equal. A square has diagonal lengths that are equal but a rhombus does not. Lastly, each of the angles of a square measure 90 degrees but opposite angles are equal for a rhombus.