This field reports the number of packet drop events on this PM instance, exposed here as cienaCesPmExtendedTxRxStatsBinDropEvents. On this Ciena CES port's PM data, this is an RMON-style drop-event counter — it counts the number of times this PM instance had to drop packets due to resource exhaustion (a full buffer or queue), not the number of packets dropped, so one burst of congestion that drops fifty packets in a row can still just register as a single event here; and this sits in the currently active extended Tx/Rx interval bin — its sibling StartTime/ClearTime fields mark exactly which window is being counted, so a change here reflects activity happening in the live collection interval, not something already filed away in history. For example, drop events climbing from 0 to just 2 on this port would already be worth a closer look, since a healthy link should hold this counter at zero.