Game concept
Activity Type
The game also links it as Activity Types.
From the game's encyclopedia
Some Activities and Grand Activities have different types corresponding to special variants of the activity.
For example, when planning a Hunt, you may choose between Standard, Falconry, and Legendary if you fulfill the requirements for that type.
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.
Activity Type is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Some Activities and Grand Activities have different types corresponding to special variants of the activity." It is part of Activity. The game also links it as Activity Types. 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.