Well, it's a new wireless data transfer specification. 802.11 is the IEEE standard for "... is a set of physical layer standards for implementing wireless local area network (WLAN) computer communication in the 2.4, 3.6, 5 and 60 GHz frequency bands" (Wikipedia), and currently there are four finalized and approved standards: A, B, G, N (not in their order of approval). The latest is N, it was only finalized a couple of years ago.
Now wireless networking makers like Belkin, etc., are advertising AC networking! Isn't that wonderful! Well, not really. First off, AC is not yet an approved, codified, standard. So lots of people are working on it, and it's guaranteed that it will change before it gets approved. Which means any equipment that you buy now that supports AC may or may not work when the standard is finalized and approved. I personally don't like throwing out equipment if I can avoid it. Second, faster networking may or may not benefit you. There are numerous bottlenecks in networking and the internet, and the biggest bottleneck is totally out of your control: it starts where your router plugs in to the wall. Internally, maybe your router is a 10/100, which means it can handle both 10 megabit per second and 100 mb/s data transfer over a wired connection, and if it's a wireless router, maybe it's a 54 mb/s router. Wow!, you think, that's really fast! Well, yes and no. If you have two computers on your network moving large files back and forth, like ISO images or video files, then yes, faster routers and faster wireless specs can be beneficial. But the bottleneck is at the wall: when your router plugs in to the cable modem or DSL router or whatever, the speed on the other side of that device drops drastically. I get about 1.5 mb/s download from my ISP, I haven't seen faster than 8 mb/s in residential installations. So internally you can sling files around pretty fast, but once you hit the actual internet, you're back down to a crawl. It's still hugely faster than the fastest dial-up modems, but most won't appreciate the speed increase.
So unless you sling huge amounts of data around your internal network between connected computers, you're not going to appreciate much of a bonus there. Of course, you might be paying for a faster internet connection, but chances are you're still going to be slower than what your router can really crank out.
Why do I mention this? At Apple's annual World Wide Developer's Conference recently they announced including AC in their new line of laptops. I believe they also have a wireless router that's AC. But this, by itself, is not a selling point. I do think that Apple will have a good enough wireless card that it can be updated when the AC spec is finalized, whenever that is, but in and of itself AC is not sufficiently compelling to replace equipment at this time.http://www.wired.com/gadgetlab/2013/06/802-11ac-apple-wwdc/