The homeworld of the warlike felinoid Kzinti, named after Larry Niven's Known Space stories and shown in Star Trek only as a label on background star charts.
Kzin is the home planet of the Kzinti, the aggressive cat-like species introduced to Star Trek in the animated episode The Slaver Weapon. Larry Niven adapted that episode from one of his own short stories, bringing the Kzinti across from his Known Space fiction, where their world is also called Kzin.
The planet has never been visited on screen. Its name appears on a star chart drawn by Michael Okuda, first displayed at Starfleet Headquarters in the Next Generation episode Conspiracy and reused as set decoration afterwards.
The Kzinti themselves are said to have fought and lost several wars against humanity. Later series refer to them in Picard's Nepenthe and through the Kzinti ensign Taylor in Lower Decks.