Game concept
Title Succession
The game also links it as Title-Specific.
From the game's encyclopedia
A Title can have its own Succession Law, which is different from that of the Holder's Realm.
Kingdoms and Empires are most likely to have a traditional Title Succession.
The Holder of the Title can add or remove Title-Specific Succession Laws, usually at the cost of Prestige
Domiciles also have their own Title Succession, which cannot be removed.
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.
Title Succession is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Title can have its own Succession Law, which is different from that of the Holder's Realm." The game also links it as Title-Specific. 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.