This counts how many times the switch tried to add a new MAC address entry to this port's address table but found the target hash bucket already full, meaning the address-lookup hardware couldn't cleanly accommodate another entry. An admin sees this counter climbing as a sign that this port's station population, while perhaps still under the raw cat2600TsPortMaxStations cap, is causing enough hash collisions to degrade lookup efficiency and increase flooding of frames that can't be matched. A rising hash-overflow count on a port serving a large VM host farm would be a signal to redistribute hosts across more ports.