Game concept
Entrenched Regency
The game also links it as Entrenched, Regency, Entrenched Regent, Entrenched Regents, Entrench, Entrenched Regencies.
From the game's encyclopedia
If a Regency lasts too long, it may become Entrenched, and the Regent becomes even more powerful compared to their Liege.
The benefits the Regent gets from the Scales of Power become much more powerful.
To end an Entrenched Regency, the Regent must accept a gift from their Liege, or the Liege must tip the Scales in their favor.
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.
Entrenched Regency is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "If a Regency lasts too long, it may become Entrenched, and the Regent becomes even more powerful compared to their Liege." It is part of Regency. The game also links it as Entrenched, Regency, Entrenched Regent, Entrenched Regents and 2 more. 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.