That indiactes that you earned a norm for the "2nd Category" title. "Norms" are ways to track exceptional performance in a tournament. Normally when you hear about them, it is for world class players making their way towards earning a GM, IM, or other such title.
Now, before you get too excited, a "2nd Category" title is what the USCF names it for the 1600 rating level. They go down to "4th Category," which is at the 1200 rating level, and each category has a range of 200 rating points. Technically, you also earned norms for 4th and 3rd category, assuming you haven't already earned those titles (which I presume you haven't, since you just got out of the provisional ratings). You don't get a "real" USCF title until you reach the 2000 level, which is the "Candidate Master," which in the past was simply called "expert."
If you're good at math or don't mind a more technical description, you can read all about it at http://www.glicko.net/ratings/titles.pdf
Hi, I am very confused. I checked my rating on USCF and my rating has a N:2 next to it. What does the N stand for?