USCIS.gov online dictionary gives the following explanation
USCIS: An abbreviation for U.S. Citizenship and Immigration Services, an agency of the Department of Homeland Security.
USCIS: A federal agency in the Department of Homeland Security that oversees lawful immigration to the United States. Its functions include:
- Granting employment authorization to eligible aliens;
- Issuing documentation of alien employment authorization;
- Maintaining Forms I-9; and
- Administering the E-Verify employment eligibility verification program.