Game concept
Hook
The game also links it as Hooks, Hooked.
From the game's encyclopedia
A Hook is a general term for a relationship between characters where one can get the other to do their will.
There are two types, Weak Hooks and Strong Hooks, which are acquired in different ways.
Hooks can be used to force through many interactions, for example Marriage proposals and Vassal Contract changes.
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.
Hook is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Hook is a general term for a relationship between characters where one can get the other to do their will." It covers Weak Hook, Perpetual Hook, Strong Hook, Favor, Blackmail and 1 more. The game also links it as Hooks and Hooked. 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.