Game concept
Situation Catalyst
The game also links it as Catalyst, Catalysts.
From the game's encyclopedia
Certain Situations transition between Situation Phases when a Situation Catalyst occurs.
A list of which Situation Catalyst are important in each Situation Phase can be found in the Situation window.
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.
Situation Catalyst is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Certain Situations transition between Situation Phases when a Situation Catalyst occurs." It is part of Situation. It covers Dynastic Cycle Catalyst. The game also links it as Catalyst and Catalysts. Patch 1.20.1.2, from game/common/game_concepts/mpo_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/mpo_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.