"Nonimmigrants are foreign nationals granted temporary entry into the United States. The major purposes for which nonimmigrant admission may be authorized include temporary visits for business or pleasure, academic or vocational study, temporary employment, and to act as a representative of a foreign government or international organization. The Department of Homeland Security (DHS) collects information on the characteristics of certain nonimmigrant admissions, those recorded on the I-94 Arrival/Departure Record. This Office of Immigration Statistics Annual Flow Report presents information gathered from the I-94 on the number and characteristics of nonimmigrant admissions to the United States in 2008. During 2008, there were 175 million nonimmigrant admissions to the United States according to DHS workload estimates. These included tourists and business travelers from Canada, Mexican nationals with Border Crossing Cards, and all admissions requiring the submission of an I-94 form. I-94 admissions accounted for 23 percent (39 million) of the total admissions. The majority (90 percent) of I-94 admissions were short-term visitors, such as tourists and business travelers, while the remaining 10 percent (3.7 million) were temporary residents characterized by a longer duration of stay, such as specialty workers, students, and nurses (see Figure 1 and Table 1). The leading countries of citizenship for I-94 admissions were Mexico, the United Kingdom, and Japan."
United States Department of Homeland Security: http://www.dhs.gov/