Game concept
Peasant Faction
The game also links it as Peasant Factions.
From the game's encyclopedia
The Peasant Faction is populated by Counties with low Popular Opinion. Unlike other Factions, this one will always revolt even if Faction Military Power is low, as peasants are generally both optimistic and illiterate... Successful Peasant Revolts will significantly lower Control in your Realm.
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.
Peasant Faction is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "The Peasant Faction is populated by Counties with low Popular Opinion." It is part of Faction. The game also links it as Peasant Factions. 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.