As a nonimmigrant class of admission, this is an noncitizen (and their spouses and unmarried minor (or dependent) children) who comes temporarily to the United States who has been accredited by a foreign government to function as an:
Ambassador;
Public minister;
Career diplomatic or consular officer;
Other accredited official; or
Attendant, servant, or personal employee of an accredited official.
Source:
USCIS Glossary,
U.S. Citizenship and Immigration Services.