This is the average of the sub-interval multicast-packet delta samples that made up the interval this historical row represents. It matters on an archived historical sample row of that same receive-counter set, kept purely for trending past intervals rather than showing the current live value because a rising average across successive history rows would indicate multicast traffic is growing steadily rather than spiking once. A multicastPacketsDeltaAvg that grows from 150 to 900 across a week of history rows on the endpoint this history row belongs to would suggest a new multicast application was turned on somewhere upstream.