From the game's encyclopedia
An Accolade's Glory increases its Accolade Rank.
Glory is gained by the Acclaimed Knight winning Battles, defeating warriors, competing in Grand Tournament Contests, and attending Activities.
However, the Accolade's Glory is lowered when the Acclaimed Knight is involved in losing battles, and may also diminish on Accolade Succession if the Acclaimed Knight did not die in battle, a duel, or some other honorable fashion.
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.
Glory is an entry of Crusader Kings III's in-game encyclopedia (Accolades). The game explains it: "An Accolade's Glory increases its Accolade Rank." It is part of Accolade. Patch 1.20.1.2, from game/common/game_concepts/04_ep2_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/04_ep2_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.