http://forums.studentdoctor.net/showthread.php?t=535664
PL is pediatric level and is our term for our training, just like anesthesia uses CA for it's training post-internship. PGY is the more general term. The linked thread has a mildly entertaining description of the difference and origin of the terms. Since pediatric training is 3 years, then beyond 3 years would go into fellowships. Since essentially all fellowships are 3 years and even allowing for a chief resident year, it would be hard to exceed PL-7 as a true training year in pediatrics. Of course, if you continue with the pedi terminology in other fields it's possible.