This counts the one-second intervals during the bin in which at least one coding violation was detected on this OTU signal. Because this reading comes from the still-filling, live 15-minute bin for this OTU signal, Errored Seconds is the standard telecom metric SLAs are written against, so this count on this specific OTU signal is often what actually determines whether a service-level threshold was breached this bin. For example, a bin with 3 Errored Seconds out of 900 seconds (a 15-minute interval) is well within most carrier-grade SLAs, whereas the same OTU signal logging 120 ES in one bin would likely breach a typical 99.999%-availability commitment, so far within this still-open 15-minute interval.