Game concept
War Target
The game also links it as War Targets.
From the game's encyclopedia
A region on the map targeted by a Casus Belli in a War. If the casus belli does not target a specific region, the Realm Capital of the defender is the War Target.
The attacking side gains more War Score by Occupying Holdings within the War Target. Conversely, the defender will — after an initial grace period — start accruing war score for holding on to all Counties in the War Target region.
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.
War Target is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A region on the map targeted by a Casus Belli in a War." The game also links it as War Targets. 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.