A word [previously] used by the U.S. government to describe a foreign-born person who is not a citizen by naturalization or parentage. People who entered the United States legally were called resident aliens and they carried alien registration cards also known as green cards, because they used to be green.
[In February 2021, Tracy Renaud, the acting leader of US Citizenship and Immigration Services, issued a memo instructing the agency’s leadership to make the following changes: to no longer refer to people as “illegal alien,” “alien,” or “undocumented alien” in internal and external communications, and to instead use the terms “noncitizen,” “undocumented noncitizen,” or “undocumented individual.”]*In modern times, with science-fiction growing in popularity, alien has come to mean a creature from outer space, and is considered pejorative by most immigrants.
*updated Feb. 17, 2021
REFERENCE: National Association of Hispanic Journalists