This counts frames known to be lost because the internal receive FIFO overflowed, typically because the device could not get sufficient PCI bus bandwidth, and notes that a single overrun can cause subsequent frames to be lost too without necessarily being counted under other error types. Because the description explicitly warns that frames lost this way will not show up double-counted in the short-frame, misalignment, or CRC counters, this object is often the more reliable indicator of an actual bus-bandwidth bottleneck on the card, a rising value here pointing at the same kind of internal bandwidth limitation as cdmipEtherTransmitDMAUnderrunCount but on the receive path instead. A card seeing sustained heavy inbound traffic that starts showing a rising count here, even while the Ethernet cabling and switch port are healthy, would point toward the card's own internal PCI or DMA bandwidth being the actual bottleneck rather than anything external.