Refers to a person who moves to another country or region to live there permanently. The direction (emigration or immigration) depends on context.
He is a migrant to Canada.
Many migrants went to America in the 19th century.
移住者 means someone who has migrated or relocated to a new place, while 居住者 simply means a current resident regardless of how they came to live there.
overseas emigrant; overseas immigrant
Compound of 移住 (いじゅう, 'migration') + 者 (しゃ, 'person').