Which is always a rhombus? Parallelogram, Trapezoid, Rectangle, or Square?
Rhombus - Four sides, all the same length, with opposite sides parallel.
Parallelogram - Four sides; two pairs of parallel sides.
Trapezoid - Four sides, with at least one pair of parallel sides.
Rectangle - Four sides connected at four right angles, thus giving two pairs of parallel sides.
Square - Four sides, all the same length, all connected at right angles.
Between mentioned figures you can write following dependencies:
Every rhombus is a parallelogram and a trapezoid.
Appart from it you can say that:
Parallelogram is trapezoid, but not every trapezoid is a parallelogram (for example a right trapezoid is not a parallelogram because it has only one pair of parallel sides)
Rectangle is a parallelogram.
Square is a rectangle, parallelogram, trapezoid and rhombus.