This is the cumulative count of bytes UCS Manager has recorded as received on this Ethernet endpoint since the counter was last reset, held as an unsigned 64-bit integer to avoid wrapping on a busy 10/40GbE link. It matters on the live receive-side counter set UCS Manager keeps for one Ethernet endpoint (a blade's vNIC adapter port, an I/O Module uplink, or a fabric-interconnect server port) inside a UCS domain because comparing this raw cumulative figure against successive polls (rather than trusting a single reading) is how bandwidth utilization on that link gets calculated. A jump from roughly 2.1 TB to 2.4 TB between two polls on this interface means about 300 GB of inbound traffic passed in that interval.