This counts otherwise-good received frames that were discarded because of unavailable resources. Unlike the CRC or alignment counters, which point at physical-layer signal problems, this points at the receiving system running out of some internal resource, like buffer memory, to actually store an otherwise valid frame, suggesting the card is being overwhelmed rather than experiencing a wiring or signal issue. A rising count here during a period of unusually high traffic volume, with CRC and alignment error counts staying flat, would suggest the card's receive buffering is being overrun by load rather than any physical-layer fault.