Game concept
Special Relation
The game also links it as Special Relations, Special Relationship.
From the game's encyclopedia
Special Relations are relationships a character has which are not bound by family or Vassalage. These Special Relations fall into several different categories, may carry Character Modifiers for the character involved, and determine what things can happen between them.
Standard Relations:
• Friend
• Lover
• Rival
• Guardian
• Ward
• Mentor
• Student
• Elder
• Disciple
Upgraded Relations:
• Soulmate
• Nemesis
Childhood Relations:
• Bully
• Victim
• Crush
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 Relation is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Special Relations are relationships a character has which are not bound by family or Vassalage." It covers Lover, Soulmate, Friend, Best Friend, Rival and 10 more. The game also links it as Special Relations and Special Relationship. 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.