Game concept
Banishment
The game also links it as Banish, Banished.
From the game's encyclopedia
Imprisoned Characters can be Banished from the Realm, which is arguably the harshest form of punishment. Banished Landed Rulers are deposed, while Banished Courtiers have their assets seized.
Banishment without a reason (e.g. some severe Crime) is considered extremely Tyrannical.
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.
Banishment is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Imprisoned Characters can be Banished from the Realm, which is arguably the harshest form of punishment." The game also links it as Banish and Banished. 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.