"Each year, millions of foreign nationals are admitted into the United States. Those who are admitted temporarily and for a specific purpose are referred to as nonimmigrants. Most nonimmigrants 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 20061 using data collected from the Arrival-Departure Record, Form I-942, of Customs and Border Protection (CBP)."
Department of Homeland Security: http://www.dhs.gov