Game concept
Confederation
The game also links it as Confederation Government, Confederations.
From the game's encyclopedia
A relation that binds Tribal or Nomadic Rulers in mutual defense, similar to an Alliance. Formed through the Call for Confederation Decision, a confederation requires its members to join each other's Defensive Wars. Confederations are visible in the Diplomacy tab.
Fellow Confederates also may not attack or Raid one another. They are restricted from high levels of Tribal Authority and Dominance, and may not create new Titles.
Confederates may use the Abandon Confederation Decision or Migrate to become Independent. If a confederation is left with only one member, it is destroyed.
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.
Confederation is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A relation that binds Tribal or Nomadic Rulers in mutual defense, similar to an Alliance." It is part of Government. It covers Confederate. The game also links it as Confederation Government and Confederations. Patch 1.20.1.2, from game/common/game_concepts/mpo_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/mpo_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.