An alien is an individual who is not a citizen of the country in which they reside. The term can be further classified into categories such as illegal alien and resident alien.
A nonresident alien is an individual who is not a lawful permanent resident of the United States during the calendar year and does not meet the requirements of the substantial presence test, nor elects to be treated as a resident alien.
A person who has been admitted to permanent resident status but has not been granted citizenship; often referred to as a 'Green Card' holder.
