This read-only Unsigned64 reports how much the aggregate receive errors count increased since the previous stats-polling interval recorded in this one archived historical sample of an interface's error-statistics, 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 admins watching this specific interface use it as the first-pass health check on its receive side before drilling into the more granular align/FCS/undersize counters for the same port. For example, a spike here on this interface is usually what sends someone to check its align and FCS counters next, which this delta field would show as a sudden nonzero reading in a single interval.