Game concept
Independent Ruler
The game also links it as Independent, Independent Rulers.
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.
Independent Ruler is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Independent Rulers have no Liege and thus enjoy greater freedom of action (e.g." It is part of Ruler. The game also links it as Independent and Independent Rulers. 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.