Game concept
Raid for Captives
The game also links it as Raids for Captives, Raiding for Captives.
From the game's encyclopedia
This is a special type of War, started by a Ruler whose Faith practices human sacrifice. The primary goal of Raiding for Captives is to do battle and capture Prisoners for sacrifice, with either side able to get enough War Score through combat to win without ever having to Siege.
At the end of the War, if the victor (including the defender) follows a Faith practicing human sacrifice, then they will take several Prisoners from the Court of the loser. If both main combatants in a Raid for Captives follow the same faith, then the war is considered sacred, meaning that the loser still receives (reduced) Piety even in defeat.
You cannot conduct or continue a Raid for Captives if you have any Prisoners obtained through winning a Raid for Captives in your Dungeon.
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.
Raid for Captives is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "This is a special type of War, started by a Ruler whose Faith practices human sacrifice." The game also links it as Raids for Captives and Raiding for Captives. 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.