Exactly as described, this is a running total of packets discarded on this benchmark port's transmit path. Unlike the errored-frame counters, discards typically represent frames the device chose not to send, for example due to output queue exhaustion, rather than frames corrupted in flight, so a rising value during a high-bandwidth test points toward the generator itself being unable to keep up with its own configured transmit rate. For example, discards climbing at a fixed test bandwidth close to the port's line rate would suggest lowering the configured test bandwidth rather than assuming the far end is the bottleneck.