What is the deportation?
Deportation (also called "removal") occurs when the federal government formally removes a foreigner from the United States for violations of a number of immigration or criminal laws, described in more detail below. Once deported, a foreigner may lose the right to ever return to the United States, even as a visitor.
Removal is a legal proceeding, and a foreigner who is subject to this procedure has legal rights prior to being removed from the country, including the right to challenge the removal itself on procedural or constitutional grounds. Following is a discussion of the removal process.
Classes of Deportable foreigner in the United States:
Is an inadmissible foreigner according to immigration laws in effect at the time of entry to the U.S. or adjustment of nonimmigrant status.
Is present in the U.S. in violation of the Immigration and Nationality Act or any other U.S. law.
Violated nonimmigrant status or a condition of entry into the U.S.
Terminated a conditional permanent residence.
Encouraged or aided any other alien to enter the U.S. illegally.
Engaged in marriage fraud to gain admission to the U.S.
Was convicted of certain criminal offenses.
Failed to register or falsified documents relating to entry in to the U.S.
Engaged in any activity that endangers public safety or creates a risk of national security.
Engaged in unlawful voting.
References:
http://immigration.findlaw.com/deportation-removal/deportation.html
http://www.jcsimmigration.com/deportation-removal-proceedings/