K'thar (also known as the Klinzhai system or Qo'noS system) is a star system located in space at the heart of the Klingon Empire. K'thar is a binary system, with primary star K'lai Klinzhai being the location of the Klingon Homeworld.

K'thar is located in the Beta Quadrant, in Qo'noS sector, in the general vicinity of Kahless system, Sif and Ikaal, and is the location of Klingon Defense Force Command Headquarters and the seat of the Klingons' Imperial government. (FASA RPG module: The Klingons; Decipher RPG module: Worlds; ST references: Star Trek Maps, The Worlds of the Federation, Star Charts; ST video games: Conquest, Star Trek Online)

The star and system referred to here was labeled as "Klingon" in Star Trek Maps, The Worlds of the Federation and the Star Fleet Technical Manual, as "Qo'noS", "Kling" and "Kronos" in Star Charts, but the Homeworld's primary star was named as "K'lai Klinzhai" in FASA's The Klingons. Star Trek Maps and Worlds of the Federation differ from other sources in stating this is a binary, with other references ignoring all but the single star the Homeworld orbits, although Decipher's Worlds specifies the overall system name is "K'thar".

During the Dominion War, the Dominion rescued a Founder from a K'tinga-class starship that was in the system. (DS9 video game: Dominion Wars)