What exactly is Usenet?

I've heard about it several times in the past year, primarily that it's going to outclass Bittorrent eventually.  But it seems I'd need an entirely new ISP or something to use it?  What exactly is it, and how does one access it?  If it makes any difference, I'm using Optimum Online.

LOL it takes me back to those heady days when people who posted shit on the network -always- lost their accounts for good. :)