Game concept
Scheme
The game also links it as Schemes, Scheming.
From the game's encyclopedia
A Scheme is a long-term attempt to affect the world around you. Schemes can target Characters, Titles, Cultures and Faiths, and come in four types: Personal, Hostile, Political, and Contract Schemes.
Your Scheme's Success Chance grows over time depending on how proficient you are in the associated Skill, and can also be impacted by the Agents you plot your Scheme with.
Secret Schemes are hidden from their target but can be discovered if their Secrecy is low.
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.
Scheme is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Scheme is a long-term attempt to affect the world around you." It covers Countermeasure Focus, Extra Measure, Hostile Scheme, Personal Scheme, Political Scheme and 15 more. The game also links it as Schemes and Scheming. 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.