This is the priority actually in effect for this egress policy right now, as opposed to the priority configured in the sibling Prio field. This is the child object that actually carries the rate limit, burst size, and priority that get applied to outbound traffic on any vNIC or vHBA using the parent QoS policy. If the configured system class named in Prio has been administratively disabled fabric-wide, UCS falls back to 'best-effort' here even though Prio still shows the original value — the mismatch between the two fields is exactly what an admin would check when traffic isn't getting the priority they expect.