The USCIS stands for the United States Citizenship and Immigration Services (USCIS). This agency exists within the United States Department of Homeland Security (DHS). The core responsibility of USCIS is to oversee the lawful immigration of aliens into the United States. The USCIS's goal is to further national security, eliminate immigration backlogs and (according to online sources) improve customer service.
The USCIS performs the administrative functions formerly performed by the US Immigration and Naturalization Services.
According to USCIS's website,
We are the 18,000 government employees and contractors of USCIS working at 250 offices across the world. Achieving our goals becomes possible when the different elements of our organization are engaged and acting as partners working toward a common outcome.
Yes, they blog too: "The Beacon"
and they tweet: "@uscis"