What is a non-square rhombus?

Any parallelogram with congruent sides whose angles ##!=90˚##.

A rhombus is a parallelogram in which all four sides are congruent (equal in length). A square is a parallelogram in which all four sides are congruent AND all four angles are right angles.

Squares are always rhombi, but not all rhombi are squares. The following is a picture of a rhombus, because all four of its sides are congruent BUT its angles are not right angles, so it is not a square.