This is the average of the periodic unicast-packet delta samples UCS Manager took across the current reporting interval. 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 trending this average over days is how an admin establishes the normal unicast baseline for capacity planning on that link. An unicastPacketsDeltaAvg that climbs steadily from 3,000 to 9,000 per sample over a month on this interface is the kind of organic growth that argues for planning additional uplink bandwidth.