Exactly. In the strictest sense, "boards" are the exam you take to obtain specialty certification. But it's common to refer to the USMLE as "boards." Not least because, even though it's the "U.S. Medical Licensing Examination," it's a product of the National Board of Medical Examiners. The test, in fact, used to be known as the NBME exam.
NBME also does the lovely shelf exams you take in third year, but calling those "boards" would probably be carrying things a bit far...