Definition from Nolo’s Plain-English Law Dictionary
A U.S. department that handles foreign relations under the leadership of the Secretary of State. Among its many functions, DOS operates U.S. embassies and consulates in other countries. Generally, the DOS determines who is entitled to a visa or green card when an application is filed outside the United States. U.S. Citizenship and Immigration Services (USCIS), under the Department of Homeland Security, regulates immigration processing inside the United States.