Game concept · By God Alone
Ecumenical Council
The game also links it as Ecumenical Councils.
From the game's encyclopedia
An Ecumenical Council is an Activity in which the top Clergy in all of Christendom gather to settle the future of the Church.
Over successive debates, the assembled prelates rule on the Tenet Status of contested Tenets — declaring them Permitted or Prohibited, or elevating them to Core — and settle the Doctrines of the Faith.
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.
Ecumenical Council is an entry of Crusader Kings III's in-game encyclopedia (By God Alone). The game explains it: "An Ecumenical Council is an Activity in which the top Clergy in all of Christendom gather to settle the future of the Church." The game also links it as Ecumenical Councils. 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.