This counter tallies packets shorter than 64 bytes received on this one port that otherwise had no errors, i.e. legitimate runts rather than collision fragments. Because standards-compliant Ethernet never sends frames under 64 bytes, a value here usually points to a diagnostic tool or non-conforming NIC attached to this specific port. An admin seeing this counter rise on one port while its group-level counterpart stays otherwise flat would go inspect exactly what device is plugged into that jack.