On site grading is when you get the cards graded at a card show rather than shipping them in. For instance, there will be on site grading at the National in August. I think it costs a little bit extra as they're doing it in a rush (depending on the number of on site orders). You might find what you're looking for here: http://www.beckett.com/grading/grading_faq
3,850+ diff Pistons cards