This is the number of multicast packets received on this endpoint during the specific 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 stored delta lets an admin later correlate a spike in this specific historical interval with a change made to multicast routing or group membership elsewhere in the network. A multicastPacketsDelta of 12,000 in one history row on the endpoint this history row belongs to, against a normal baseline of 200, would prompt a check of IGMP group membership changes around that timestamp.