PGY-1 = Post Graduate Year 1 (also a first yr resident or what is commonly called your intern year.
PGY-2 = 2nd yr resident
Some programs don't have PGY1s, such as Rads, etc., where they want you to do your intern year in another field, like IM, then you don't start your 'true' radiology residency until you are PGY-2. I guess these PGY-2s would be first yr radiology residents? Or would you still call them 2nd yr? Dunno, feel free to correct me if I am wrong...