This read-only Unsigned64 gives the average per-interval delta of output discards 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 a rising count here on this port almost always means its outbound queue is filling faster than the link can drain, i.e. this specific uplink or interface is oversubscribed or congested. 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.