In short, it is discussion forums within the Google+ network but obviously, Google+yfied.
It launched and started rolling out last night and over night, I had like 50 different Google+ Community invites. It was a bit overwhelming. That being said, I wonder if all of Google's forums - the Google Groups, the Google Help forums - if they will switch to it?
Here is a video on the new feature:
If you have any feedback you want to share about this new feature, you can do so at Google+ Help.
Forum discussion at Google+ Help.