This counts packets that arrived on this interface but were discarded before being forwarded, distinct from packets rejected for being malformed. A climbing InDiscards count for the current, still-accumulating short interval bin on this port without a matching rise in RxInErrorPkts points at resource starvation on this specific interface -- a full receive queue or an active policer/rate-limit -- rather than at a bad cable or noisy signal. For example, InDiscards jumping to 120 during this in-progress short-interval bin on a port that's also showing high RxFramesPerSec suggests this interface's ingress buffer is being overrun by a burst faster than the switch can queue it.