This is the average value over the current performance-monitoring interval of the residual bit error ratio measured after forward error correction has attempted to fix the errors detected on the incoming signal, expressed as a bit-ratio. An average that stays at or near zero over the monitoring interval confirms FEC is comfortably keeping up, while any sustained non-zero average shows the link is operating beyond FEC's correction capability for at least part of the interval. For example, a customer reporting occasional data corruption on a service would have an admin check bitErrorRatePostFecAvg for that port to see whether errors are consistently slipping through FEC rather than being a one-off event.