This read-only Unsigned64 gives the average per-interval delta of aggregate receive errors across all the sampling intervals collected so far for this interface's live, currently-active error-statistics record, smoothing out interval-to-interval noise. Admins trend this average over time on a given link to tell a persistent, low-grade problem from a one-off blip, 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. An average that creeps upward release over release on the same port, even while individual deltas look small, is the kind of slow drift that justifies scheduling a cable or optic replacement.