A post-graduate (PG) year is a year beyond high school graduation, spent at an independent school. Some students choose an additional year of high school in order to build their student study and time management skills with another year of academic preparedness, it allows a student to mature socially and/or academically, perhaps another year to strengthen athletic ability to pursue a sport in college. Some students know early on that they would like to pursue a PG year and don't go through the college application process. Others, decide to expand their options and consider both a PG year and college.
Many independent schools offer a PG option to a small cohort of students who are essentially members of the senior class. As post-graduates, these students will have already earned a high school diploma so they will be making academic choices that will enhance their profile for college by filling in gaps on their transcript or taking some more advanced courses. Some schools will have one or two required courses for their post-graduate students.
More information and a list of PG Programs is available: Post-Graduate Schools