This counts frames received on the port that the switch had to forward onward -- either to another port or up to the system module -- because their destination wasn't local to this port's segment. An admin tracks this to gauge how much inter-segment traffic a given port generates, which matters for capacity planning on the switch's internal backplane or uplink. A steadily climbing count on one port relative to its neighbors might indicate that segment has become a traffic hot spot needing its own dedicated uplink.