Game concept
Battle
The game also links it as Battles.
From the game's encyclopedia
Battles start when two opposing Armies enter the same Barony.
At the start of a Battle, one side usually starts with Advantage dependent on factors like Terrain, Commander and Commander Traits.
Armies take Casualties based on the amount of Damage sustained. The Battle enters its Aftermath when no Soldiers remain for one side.
The winner of a Battle is awarded War Score dependent on the magnitude of the victory.
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.
Battle is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Battles start when two opposing Armies enter the same Barony." The game also links it as Battles. 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.