Game concept
Occupation
The game also links it as Occupy, Occupying, Occupied, Occupations, Occupies.
From the game's encyclopedia
Occupied Holdings are temporarily under the control of a hostile Ruler during a War. An Army standing in a Barony with a hostile Fortified Holding will start to Besiege it if the number of Soldiers in the army outnumbers the Garrison.
If the Siege is successful, the Holding is Occupied, which will give War Score to the Occupying side in the War.
Occupying a Holding does not mean it is now yours! Only territory specified by the War Target can actually change hands, and only if the Attacker Wins.
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.
Occupation is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Occupied Holdings are temporarily under the control of a hostile Ruler during a War." The game also links it as Occupy, Occupying, Occupied, Occupations and 1 more. 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.