Game concept
Legend
The game also links it as Legends.
From the game's encyclopedia
A Legend represents the important deeds that a Character achieved in life, and are created from Legend Seeds.
Legends are powerful ways to obtain Legitimacy, and other possible rewards like Skill increases, Opinion bonuses, Renown, Prestige or Piety. Baronies in which a Legend has spread may also receive additional effects, if held by the Legend owner or a Legend Promoter.
Legends have a Legend Type that governs those rewards: they can be Legitimizing, Holy or Heroic. Each Legend also has a Legend Quality level, which influences the strength of those rewards, as well as its spread.
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.
Legend is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Legend represents the important deeds that a Character achieved in life, and are created from Legend Seeds." It covers Owned Legend, Promoted Legend, Legend Seed, Legend Quality, Legend Protagonist and 3 more. The game also links it as Legends. Patch 1.20.1.2, from game/common/game_concepts/06_ce1_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/06_ce1_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.