Alien (law)
 

In law, an alien is a person who is not a native or naturalized citizen of the land where they are found. Types of "alien" persons are:

• An alien who is legally permitted to remain in a country (which is foreign to him/her) on specified terms may be called a "legal alien" of that country.
• An alien who has temporary or permanent residence in a country (which is foreign to him/her) may be called a "resident alien" of that country.
• A visitor with the legal right to visit a country (which is foreign to him/her) may be called a "nonresident alien" of that country.
• The term illegal alien describes a foreign national who resides in another country unlawfully, either by entering that country at a place other than a designated port-of-entry or as result of the expiration of a non-immigrant visa. (See illegal immigration)
• An enemy alien is an alien who is designated as an enemy. (See enemy combatant).

http://en.wikipedia.org/wiki/Alien_(law)