This counts reliable, acknowledgement-required, EIGRP unicast packets sent to peers on this interface, typically retransmissions or updates directed at one specific neighbor rather than the whole segment. Because EIGRP falls back to unicast retransmission when a multicast packet is not acknowledged by a particular peer, a rising count here concentrated on one interface points to a specific neighbor missing multicast packets rather than a general link problem. If this counter climbs sharply while cEigrpRMcasts stays flat, that pattern specifically indicates one neighbor is failing to receive multicast updates and is being serviced by unicast retries instead.