It lists the most-cited papers that were published at one of many conferences, and then also which paper received the “best paper” award at that conference. Frequently, the “best paper” is far from being the most influential (or at least, far from being cited most often).
I guess that shows how difficult it is to predict the impact of someone’s work. It also makes me feel a little warm and fuzzy, though, because I do know most of the top and best papers from recent PLDI conferences. I guess I’ve retained a few things from my PhD work.