Immigration was the movement of individuals to a location they did not originate from.
In 2370, approximately three million Skrreea made a request for immigration to Bajor's provisional government. After much debate, it was denied, on the grounds that Bajor was still recovering from Cardassian occupation. (DS9: "Sanctuary")
In 2373, Minister Odala rebuffed Gegen's claims that the Voth originated elsewhere, protesting, "We are not immigrants!" (VOY: "Distant Origin")