Game concept
Theocracy
The game also links it as Theocracies, Theocratic, Theocratic Government.
From the game's encyclopedia
Theocracy is a Government Form available for some Faiths depending on Doctrines. They are usually lead by a Head of Faith or a Landed Realm Priest. A Bishop might also become an Independent Theocratic ruler in their own right.
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.
Theocracy is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Theocracy is a Government Form available for some Faiths depending on Doctrines." It is part of Government. It covers Theocratic Vassal. The game also links it as Theocracies, Theocratic and Theocratic Government. Patch 1.20.1.2, from game/common/game_concepts/00_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/00_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.