Game concept
Commander Trait
The game also links it as Commander Traits.
From the game's encyclopedia
Commander Traits are special Traits that confer useful perks to characters when acting as Army Commanders.
Commander Traits are typically acquired by children raised with the Martial Education Focus, but can also be gained through the Martial Lifestyle and other means.
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.
Commander Trait is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Commander Traits are special Traits that confer useful perks to characters when acting as Army Commanders." It is part of Trait. The game also links it as Commander Traits. 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.