Game concept
Command Modifier
The game also links it as Command Modifiers.
From the game's encyclopedia
This Modifier is only active for Commanders.
If a character with a Command Modifier commands an Army, it will get this effect.
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.
Command Modifier is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "This Modifier is only active for Commanders." The game also links it as Command Modifiers. 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.