This is the live, still-accumulating count of bytes that forward error correction has successfully repaired on this DWDM trunk interface during the interval that's currently in progress, as opposed to a completed historical interval. It is the real-time value an engineer compares directly against cMsDwdmFECThreshByteErrCor to see how close the link currently is to tripping a degraded-signal alarm, ahead of the interval closing out. Watching this counter climb rapidly partway through its interval, well before historical intervals would suggest, is an early sign of an optical path degrading faster than usual, worth investigating before the alarm threshold is actually crossed.