Game concept
Migration
The game also links it as Migrate, Migrates, Migrated, Migrating.
From the game's encyclopedia
Migration is essential to Nomads. When the County Fertility in their Realms is low they will often move in search of greener pastures.
Migration can only target De Jure Titles and the accessible Tiers are limited by a Ruler's Dominance.
A proposal will be sent to the Nomad with the biggest Herd in the desired area, and they can decide whether to leave their lands willingly, or to go to war to defend them.
Herders will always leave their lands, as they do not have the means to defend themselves.
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.
Migration is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "Migration is essential to Nomads." The game also links it as Migrate, Migrates, Migrated and Migrating. 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.