The proper name of the Klingon Homeworld is Kronos but the formal name, Q'onoS, is capitalized when written.  Green in color, it is a planet of the star Klingon and the site of the Imperial Empire's capital First City.

It includes a lone large land mass with a vast ocean, with a severely tilted axis that causes wild seasonal changes, a turbulent atmosphere and extremes of both warm and frigid weather.

The capital city remains neutral to both sides during the empire's civil war, and even houses Sela and Movar. It is within hailing distance after a day out at an unspecified warp speed from Vulcan.  Direct communication is possible at least within four days' travel at warp.