Game concept
Title Claim
The game also links it as Title Claims, Claim, Claims, Claimed.
From the game's encyclopedia
A Claim on a Title represents a legal right to own it and provides a Casus Belli to conquer it through War. Claims also provide a valid reason to Revoke Titles off Vassal Holders.
Claims are usually given to Rulers whenever they lose control of Titles to someone else, but can also be created through the Fabricate Claim Task.
Furthermore, each child (even Bastards) of a ruler has an Implicit Claim on all of that ruler's Titles. If they do not inherit that title from the Ruler when they die, those Implicit Claims will convert to Pressed Claims, which can then be inherited by their own children as Unpressed Claims.
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 Claim is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Claim on a Title represents a legal right to own it and provides a Casus Belli to conquer it through War." The game also links it as Title Claims, Claim, Claims and Claimed. 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.