This read-only Counter64 reports the number of packets that were tail-dropped, discarded because a queue was full, on an interface. A nonzero or growing value here is a direct sign of congestion on that interface's queues, which matters for diagnosing application slowness or packet loss complaints. For example, an admin troubleshooting a user's complaint about choppy video calls would check this counter on the relevant interface to confirm whether queue drops are the cause.