Game concept
Estate Building
The game also links it as Estate Buildings.
From the game's encyclopedia
Estate Buildings are unique and persistent improvements to a Noble Family's Estate.
A large variety of structures are available for construction and may be built by the Estate's owner to generate private income, expand the family's Influence, and gain access to a number of Decisions, Interactions, and more.
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.
Estate Building is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Estate Buildings are unique and persistent improvements to a Noble Family's Estate." It is part of Domicile Building. The game also links it as Estate Buildings. Patch 1.20.1.2, from game/common/game_concepts/07_ep3_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/07_ep3_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.