Game concept · The Fate of Iberia
Iberian Reclamation
The game also links it as Iberian Reclaiming, Iberian Reclamations.
From the game's encyclopedia
This is a special type of War available to Involved Rulers of the Iberian Struggle.
The attacker aims to conquer a Duchy which contains any Involved Counties held by an Interloper or Uninvolved Ruler, or Vassalize them if they hold no land outside that Duchy.
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.
Iberian Reclamation is an entry of Crusader Kings III's in-game encyclopedia (The Fate of Iberia). The game explains it: "This is a special type of War available to Involved Rulers of the Iberian Struggle." The game also links it as Iberian Reclaiming and Iberian Reclamations. Patch 1.20.1.2, from game/common/game_concepts/03_fp2_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/03_fp2_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.