This counter tracks the number of BGN (Begin) PDUs received on this port, per the description, marking each time the far end has initiated (or reinitiated) SSCOP signaling-link establishment toward this port. Comparing this to NumBgnPduTx tells you which side is more often the one restarting the link, which matters when troubleshooting a signaling channel that keeps resetting -- a far end repeatedly sending BGN suggests the instability is on their side rather than this port's. Frequent unexplained BGN receipt is worth escalating to whoever manages the peer switch.