This read-only PerfCounter64 counts Severely Errored Framing Seconds encountered by this SONET/SDH Section in the current bin, per its source description, meaning seconds where the section layer lost frame alignment badly enough to be classified severely errored. A rising count tells an administrator the interface is having trouble maintaining basic frame synchronization, a more fundamental problem than ordinary bit errors. For example, persistent ocnStmStatsSectionSEFs activity alongside a link that keeps dropping and reacquiring frame sync would point to a hardware or clocking problem on that line card.