The long-rumored "Google +1" is no longer rumored. It's fact, and it's been formally announced by Google. To but it bluntly, it's Google's version of the Facebook Like button. You'll find it on search results, ads, and eventually on sites all over the web.
Here's a video with a quick description:
Again, it's pretty much Google's version of the "like", which could eithe turn out to be really, really huge, or a massive dud. We'll see.