Game concept
House Relation
The game also links it as House Relations.
From the game's encyclopedia
When two Houses interact they may develop a positive or negative House Relation, which remains over the generations.
Beyond affecting the Opinion of all House members, each House Relation level may have extra effects, such as making Alliances and Wars easier or harder to effect.
The House Relation remains at the same level until the sum of all actions reach either +100% or -100%. Then, the House Relation is moved to the next level, either positive or negative.
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 Relation is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "When two Houses interact they may develop a positive or negative House Relation, which remains over the generations." The game also links it as House Relations. Patch 1.20.1.2, from game/common/game_concepts/tgp_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/tgp_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.