This read-only Counter64 reports how much the deferred transmissions count increased since the previous stats-polling interval for this interface's live, currently-active error-statistics record, i.e. the per-interval rate rather than the lifetime total. A nonzero value here means new failures of this specific kind are occurring right now on this link, not just accumulated history, since on the full-duplex fabric and adapter uplinks UCS uses this should stay essentially at zero, so any real growth here points at an unexpected half-duplex negotiation or a badly oversubscribed shared segment on this specific link. For example, seeing this climb by hundreds per interval on what's supposed to be a full-duplex 10G uplink is reason enough to recheck the port's negotiated duplex setting, which this delta field would show as a sudden nonzero reading in a single interval.