"Each year, millions of foreign nationals are admitted into the United States. Those who are temporarily admitted for a defined period of time and for a specific purpose are referred to as nonimmigrants. Most non-immigrants enter as tourists or business travelers on short-term trips, while others, such as students, temporary workers, and foreign diplomats, stay for longer periods of time, ranging from a few months to several years. This Office of Immigration Statistics Annual Flow Report examines the number and characteristics of nonimmigrant admissions in 2004 recorded by the Nonimmigrant Information System (NIIS) of the Department of Homeland Securitys (DHS) U.S. Customs and Border Protection (CBP)."
U.S. Citizenship and Immigration Services: http://uscis.gov/