Game concept
Councillor
The game also links it as Councillors.
From the game's encyclopedia
Councillors are the primary assistants of any Ruler, and make up the Council. There are six positions on the council: Chancellor, Marshal, Steward, Spymaster, Court Chaplain (or Realm Priest), and finally your Spouse.
Each is in charge of a department that can be given different Councillor Tasks to perform.
Powerful Vassals will be upset if not appointed to one of these positions, meaning you often have to make a choice between placating a powerful vassal or appointing someone who is actually competent.
Serving as a Councillor to your Liege gives you a bonus, which increases with the Rank of the Liege.
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.
Councillor is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Councillors are the primary assistants of any Ruler, and make up the Council." It covers Spymaster, Steward, Chancellor, Marshal, Court Chaplain and 3 more. The game also links it as Councillors. 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.