This is the average of the sub-interval jumbo-frame 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 steady, nonzero average confirms large-MTU storage or backup traffic was flowing consistently through that interval. A jumboPacketsDeltaAvg of 1,200 on the endpoint this history row belongs to during a scheduled backup window is the expected signature of large sequential transfers using jumbo frames.