Kzin was an inhabited planet in the Alpha Quadrant. This was the homeworld of the Kzinti, a warp capable species. Its location in the Milky Way Galaxy was depicted on a Federation star chart in 2293. (TAS: "The Slaver Weapon"; Star Trek VI: The Undiscovered Country, production art)
In the mid-to-late 21st century, Kzin and Earth fought a series of four wars, in what was collectively known as the Earth-Kzin Wars. Kzin was always the aggressor and Earth was always the victor. Following the signing of the Treaty of Sirius, the Kzin government, including all Kzinti territories, was demilitarized. The Kzinti were forbidden to possess weapons or starships – except for police vessels, which were to be used solely for peacekeeping.
In 2269, two Slaver stasis boxes were discovered by archaeologists on Kzin. Kzinti privateers, secretly supported by the Highest of Kzin, hoped to discover a weapon, to defeat the Federation. The Slaver weapon however self-destructed before the Kzinti could use it against the Federation. (TAS: "The Slaver Weapon")