Per its DESCRIPTION, this Counter64 counts one-second intervals where the Section-layer error density crossed the severity threshold (a burst of B1 BIP-8 errors) or an outright defect such as loss of frame was present. Because this is a lifetime counter that only resets on an explicit clear, a reading here means section-layer errors clustered badly enough in one second to count as severe on this OC-n (SONET) port, accumulated over the port's entire service life, not merely since the last reboot. For example, 4 severely errored seconds by itself is not alarming, but a steady climb over consecutive lifetime polls points at a degrading optical connector or amplifier rather than a one-off glitch.