Zantos was a planet located somewhere in the space of the galaxy's Alpha or Beta Quadrants.
History and specifics[]
Zantos was the homeworld of the Zantosians, a garrulous, ill-tempered civilization well known for their ale. Starfleet avoided Zantos after an incident, some time prior to the late 24th century, in which the leader of an away team was captured and castrated.
According to one rumor, Mackenzie Calhoun, having made a bet with a Starfleet admiral during a drinking contest, snuck onto Zantos, acquired a case of Zantosian ale and departed with the Zantosian fleet in hot pursuit. (NF novel: Into the Void)