This is a rotational state in which the pelvis and torso face the same direction the skis point.  In it's purest form, skiing square is not something that often done, because the benefit of outside foot pronation is lost.  At least a small amount of counter is needed to properly pronate the outside foot and direct pressure to the turning edge of the outside ski.  As a contrast drill, used for feeling and becoming competent skiing in various rotational states, it's a valuable thing to practice.   When skiing low edge angle turns, whether steered or carved, positions close to square that contain only the minimum amount of counter needed to pronate the outside foot is a very efficient rotational state to employ.