This is a Counter64 preserving the total packets dropped by a now-expired control tunnel during receive processing over its entire lifetime, per its description, the historical companion to the live cisgIpsSgTunInDropPkts. A high final value here for a tunnel whose HistTermReason shows a failure (rather than normal or operator-requested termination) would suggest receive-side packet loss on this device may have contributed to that connection's eventual demise. An admin building a case for why a specific past connection was unstable would check this alongside the termination reason to build the fuller picture.