Game concept
Fatal Casualties
From the game's encyclopedia
During Battle, many (but usually not most) Soldiers are killed or too badly wounded to ever fight again. These are permanent Casualties as opposed to merely Routed Casualties.
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.
Fatal Casualties is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "During Battle, many (but usually not most) Soldiers are killed or too badly wounded to ever fight again." It is part of Soldiers. 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.