The keeping of something out of a set. Exclusion is a judgment and should be stated rather than silent.
Latin excludere, ex- (out) plus claudere (to shut); the noun for the keeping-out.
Its root is the same shutting that gives close and cloister: claudere meant to shut a door, not merely to leave someone off a list. Exclusion is that same closing act, and a closed door makes a sound — which is why this house asks that the closing be stated, not left silent.