This counter reports the total frames of Layer-2 multicast traffic on this port that exceeded the configured flood/storm-control threshold and were therefore dropped rather than forwarded, during everything accumulated since the last manual clear. Because this figure accumulates over the period since the last manual clear and is only zeroed when an operator issues a manual clear, a step-change in an otherwise-flat trend is the storm-control mechanism's record that a Layer-2 multicast flood happened on this port, caused by an unregistered multicast stream that no IGMP membership ever pruned to specific ports, and that record persists until someone deliberately clears it. For example, if this clearable total shows a jump of several thousand frames but its uncleared TotalStats-bin counterpart shows the same jump plus an older one this Stats bin no longer reflects, that difference tells you an operator cleared this counter sometime after the older Layer-2 multicast flood but before the more recent one.