From the Document: "This report presents estimates of the size and characteristics of the population of nonimmigrants residing in the United States in fiscal year 2015. Nonimmigrants are foreign nationals admitted into the United States for specific, temporary purposes. Examples of such temporary purposes include tourism, work, study, participation in an exchange program, representing a foreign government or international organization, and accompanying a principal nonimmigrant as an immediate family member or, in some cases, as a member of the principal nonimmigrant's staff. This report focuses exclusively on nonimmigrants admitted for purposes associated with residence, such as work and study, and excludes nonimmigrants admitted for non-residential purposes, such as tourism."
U.S. Department of Homeland Security: https://www.dhs.gov/