On a TCAS2 (Traffic Collision Avoidance System) the preventive " resolution advisory" (RA) is a " resolution advisory" :
asking the pilot to modify the heading of his aircraft
asking the pilot to modify the speed of his aircraft
asking the pilot to modify effectively the vertical speed of his aircraft
that advises the pilot to avoid certain deviations from the current vertical rate but does not require any change to be made to that rate