operation between the Vector3

who can tell me what is geometric meaning of operation between the Vector3

like this:

        Quaternion rotation=Quaternion.Euler(y,x,0);
        transform.rotation=rotation;
        transform.position=rotation*new Vector3(0,0,-100)+Vector3.zero;

"+ Vector3.zero" definitely will change nothing.

While "rotation*new Vector3(0,0,-100)" rotates point (0,0,-100) with a rotation.