A loose term for several Siberian languages that have in common only that they don't appear to be related to any other languages in the wider world. But they don't have any detectable genetic relationship to each other, either, so the term is not a very good one to use. None of them has any significantly large number of speakers. They are
and sometimes including also
Some linguists try their damnedest to connect even isolates with distant groups. If they are to be believed, Yenisei is closer to the great Sino-Tibetan group, Yukaghir is distantly related to the Uralic group, and the rest may possibly be connected at some level with the common run of Eurasian languages in the Nostratic macrofamily.