Game concept
Ecclesiastical
The game also links it as Ecclesiastical Government.
From the game's encyclopedia
Ecclesiastical is a Theocratic Government Form held by Christian Clergy Rulers, such as Bishops and Archbishops.
Most Ecclesiastical rulers are theocratic Vassals who Lease their Temple Holdings from a secular Liege and answer to the Head of Faith, although a Bishop who possesses Landed Titles that are not Leased may rule as an Independent Ecclesiastical Ruler in their own right. The power such a ruler holds over their own Vassals is determined by their Church Authority.
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.
Ecclesiastical is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Ecclesiastical is a Theocratic Government Form held by Christian Clergy Rulers, such as Bishops and Archbishops." It is part of Government. It covers Papabile Score. The game also links it as Ecclesiastical Government. Patch 1.20.1.2, from game/common/game_concepts/pam_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/pam_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.