Game concept
Temple Citadel Holding
The game also links it as Temple Citadel, Temple Citadels, Temple Citadel Holdings.
From the game's encyclopedia
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.
Temple Citadel Holding is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Temple Citadels are a pragmatic mix of the Castle fortification and the Temple worship — it is the standard Holding Type for Mandala Rulers." It is part of Holding Type. The game also links it as Temple Citadel, Temple Citadels and Temple Citadel Holdings. 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.