A girl starts from a point P and walks 10 meters in the North-West direction and reaches the point Q. She then turns to her left and walks 10 meters to a point R which is directly west ward to point P. She again turned to her left and walks 10 meters and reaches a point S which is directly southward to point Q. From the point S she turns towards point P and walks 10 meters. What is the shape of the geometrical figure PQRS?