Game concept
Spiritual Head of Faith
The game also links it as Spiritual.
From the game's encyclopedia
A Spiritual Head of Faith is Theocratic and does not have to be Landed (although they can be).
Spiritual Heads of Faith usually have access to interactions such as being able to grant Claims or Gold.
Should the Doctrines of the Faith allow for Great Holy Wars then they will be Undirected (e.g. Crusades).
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.
Spiritual Head of Faith is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Spiritual Head of Faith is Theocratic and does not have to be Landed (although they can be)." It is part of Head of Faith. The game also links it as Spiritual. 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.