Game concept
Claimant
The game also links it as Claimants, Claimant's.
From the game's encyclopedia
A Claimant is a person with one or more Claims to Titles. Ruler Claimants can press these by using the Claim Casus Belli to declare Wars.
This Casus Belli can also be used to press the Claims of Vassals and even Unlanded characters in your Realm.
Claimants can also lead Factions — even if they do not reside in your Realm.
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.
Claimant is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Claimant is a person with one or more Claims to Titles." The game also links it as Claimants and Claimant's. 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.