^^^It just denotes a CPU architecture originally developed by Intel. Most PC's, whether Intel or AMD equipped, are x86. The name comes from the earlier processors which model numbers ended in "86" (as in 386, 486, etc.). They employ CISC design, as opposed to the RISC design typical in Macs. (It has to do with how the processor executes instructions/commands.) But both are so far advanced nowadays that there isn't a whole lot of real world difference between them. Nothing the average person needs to know, but you can Google the terms if you really wanna get geeky.
Nice setup for a rig, by the way. IMHO, 2 things I would keep an eye on: The PSU has gotten a couple of iffy reviews; I would go with Antec or Enermax if it gets flaky. And the heatsinks provided with AMD processors are crap if you'll be doing a lot of cpu intensive work; you may want to change that out in the future