Game concept
Special Soldiers
From the game's encyclopedia
Special Soldiers are not like regular Armies, as they are not raised from a Holding. Special Soldiers can be gained through Events, and represent various things such as retinues, ravenous hordes and ambitious peasantry.
Normally they do not cost maintenance, and do not reinforce. Use them wisely if you have them.
Several historical Rulers start with Special Soldiers.
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.
Special Soldiers is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Special Soldiers are not like regular Armies, as they are not raised from a Holding." 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.