Exactly as described, this is a running total of broadcast packets transmitted by this benchmark port. Like the multicast counter, a benchmark generator's test frames are unicast by design, so a rising broadcast count here would flag ARP or other broadcast chatter sharing the test port rather than the benchmark payload itself affecting throughput measurements. For example, a handful of broadcast packets appearing alongside millions of unicast test frames is likely just periodic ARP traffic and not a cause for concern about the test's validity.