Non-immigrant visa status allows the holder of the status to enter or remain in the United States for a particular specialized purpose.
The non-immigrant types include visitors for pleasure and business, students, professional workers, intra company transferees, religious workers, artists and entertainers, individuals with extraordinary ability, investors or traders, exchange visitors, fiancées, Free Trade professionals, and others.
The status is obtained either by making application at the US Consulate in the foreign country for permission to enter the United States in the particular status or by requesting an extension or change of status from the applicable Immigration and Naturalization Service Processing Center
Most non-immigrant visas allow their holder multiple entry to the United States. This means that one can go in and out of the United States as many times as one needs until his or her visa expires. Some allow only a single entry.