Game concept
Ecclesiastical Estate Building
The game also links it as Ecclesiastical Estate Buildings, Cathedral Complex Building, Cathedral Complex Buildings.
From the game's encyclopedia
Ecclesiastical Estate Buildings are unique and persistent improvements to a Ecclesiastical Estate.
A large variety of structures are available for construction and may be built by the holder to generate private income, Piety, Spiritual Fulfillment, and gain access to a number of Decisions, Interactions, and more.
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 Estate Building is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Ecclesiastical Estate Buildings are unique and persistent improvements to a Ecclesiastical Estate." It is part of Domicile Building. The game also links it as Ecclesiastical Estate Buildings, Cathedral Complex Building and Cathedral Complex Buildings. 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.