Game concept
Excommunicated Ruler
The game also links it as Excommunication War.
From the game's encyclopedia
In an Excommunication War, the attackers are fighting to remove an Excommunicated ruler from power.
If victorious, the attackers will gain a large amount of Piety and the approval of their Head of Faith, while the Excommunicated ruler is forced to abdicate to their Heir.
However, if the Excommunicated ruler wins, their Head of Faith is forced to revoke their Excommunication, as they have proven their righteousness on the battlefield.
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.
Excommunicated Ruler is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "In an Excommunication War, the attackers are fighting to remove an Excommunicated ruler from power." The game also links it as Excommunication War. 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.