A non-immigrant  is a foreign national seeking to enter the United States temporarily for a specific purpose. Nonimmigrants enter the U.S. for a temporary period of time, and once in the U.S. are restricted to the activity or reason for which their visa was issued. They may have more than one type of nonimmigrant visa but are admitted in only one status.  

An immigrant is a foreign national who has been granted the privilege of living and working permanently in the United States. You must go through a multi-step process to become an immigrant. In most cases, USCIS must first approve an immigrant petition for you, usually filed by an employer or relative. Then, an immigrant visa number must be available to you, even if you are already in the United States. After that, if you are already in the United States, you may apply to adjust to permanent resident status (If you are outside the United States, you will be notified to go to the local U.S. consulate to complete the processing for an immigrant visa.)