Aliens are people residing in a country of which they are not a citizen. A college student who lives in a foreign country while he or she studies could be an alien. Most aliens have intentions of relocation (
Kerry). An alien is "legal" if s/he applied for and received a NONIMMIGRANT Visa, a temporary status that is given to people who temporarily reside in another country with no intentions of permanently living there. 
When it expires, the holder must relocate. The NONIMMIGRANT Visa may not be renewed or converted to a Green Card (Wright). Many aliens overstay their Visa because they are unable to return to their country.

Immigration & Jobs