The little squares in each corner mean right angle. Yes, because a square is just a rhombus where the angles are all right angles. A square has equal sides (marked s) and every angle is a right angle (90°) also opposite sides are parallel.

It is more common to call this shape a rhombus, but some people. Webis a square a rhombus? It is often said that a square is a rhombus, but a rhombus isn’t always a square because a square fulfills all.