Immigration and Naturalisation Services. They changed the name twice in the past two years, first to BCIS (Bureau of Citizenship and Immigration Services) and now to USCIS (United States Citizenship and Immigration Services). Usually when dealing with people on the phone it's easier to say INS, people seem to know what that acronym means, unlike the new one that nets you blank stares sometimes.

But I'm not an American, just married to one, so working on residency stuff.