The homeworld of the Tzenkethi, a power that once fought a war with the Federation, and the supposed scene of a coup that a Changeling infiltrator invents in order to provoke a new conflict.
Tzenketh is the home planet of the Tzenkethi, whose territory lies within reach of Deep Space 9 and who fought a war against the Federation some years before the station came under Starfleet administration.
In The Adversary, a man claiming to be Ambassador Krajensky tells the newly promoted Captain Sisko that there has been a coup on Tzenketh and that the Defiant must patrol the border as a show of strength. The story is a fabrication: Krajensky is a Changeling who sabotages the ship and tries to use it to start a war.
The planet itself is never seen, and the Tzenkethi war is recalled again in Homefront and Paradise Lost, where Sisko's service under Leyton during that conflict is discussed.