An episode of a regular series which, for some reason, is not included when the series is shown in syndication. This can take one of two flavors: * An episode which was produced but never shown. * An episode which was shown during the initial run, but never rebroadcast. In this case, the episode is not rebroadcast because no one has it anymore. Such episodes are lost to history until (as becomes increasingly unlikely) they unexpectedly turn up in the hands of a collector or a relative of one of the original producers.