This read-only Counter counts unicast frames on this port that had to be punted to the system module specifically because the source or destination station address wasn't in the port's own forwarding table yet. A steady baseline here is normal during station learning, but a sustained high rate points at a table that can never stabilize, often because of demand aging settings that are too aggressive, or genuinely more unique stations than the table can retain. This counter is the per-port explanation for switch-wide software-load counters like ciscoTsStackSwitchRcvdFrames climbing.