Game concept · All Under Heaven
Celestial Government
The game also links it as Celestial, Celestials.
From the game's encyclopedia
Celestial is a Bureaucratic Government Form in which the Liege appoints characters as Governors, of which there are two types, Civilian and Military.
Characters have access to Influence, Noble Families, Family Mansions, and Treasury.
Independent Rulers have Legitimacy, while Vassals focus on obtaining Merit.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Celestial Government is an entry of Crusader Kings III's in-game encyclopedia (All Under Heaven). The game explains it: "Celestial is a Bureaucratic Government Form in which the Liege appoints characters as Governors, of which there are two types, Civilian and Military." The game also links it as Celestial and Celestials. Patch 1.20.1.2, from game/common/game_concepts/tgp_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/tgp_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.