This is the cumulative undersized (runt) frames received counter: counts inbound FC frames that were shorter than the minimum legal FC frame size and were rejected. On one specific historical error-statistics snapshot for an FC port, this is the lifetime tally, so runts on FC, like runts on Ethernet, usually indicate a physical-layer problem truncating frames rather than a configuration issue. For example, a port begins logging small numbers of runt frames the same week its SFP starts also reporting rising CRC errors, together pointing at a failing transceiver.