Game concept
House
The game also links it as Houses, House's.
From the game's encyclopedia
A House is a branch of members on the bigger tree of a Dynasty. Houses are created by Rulers who no longer wish to answer to their current House Head and would rather be the Head of a new House.
Although Houses have their own names and Coats of Arms, they still share Renown, and other members of the Dynasty can still be your Player Heir.
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.
House is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A House is a branch of members on the bigger tree of a Dynasty." The game also links it as Houses and House's. 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.