Why is a rhombus a rectangle but a rectangle is not a rhombus?

A rhombus is a type of parallelogram where all sides are equal in length, and it can have right angles, which means it can be classified as a rectangle if those right angles are present. However, a rectangle is defined as a parallelogram with right angles but does not require all sides to be equal; therefore, not all rectangles can be rhombuses. Essentially, while all rhombuses can be rectangles when they have right angles, rectangles do not necessarily meet the criteria to be rhombuses.