Web 2.0?? What is that?

So, I started out...What in the virtual-web-world is Web 2.0? That is why I took this class. I know there is so much out there to use in teaching- so much to promote the idea of teaching as an experience, as a creative endeavor, rather than teaching as strictly an input of ideas....but where is it..and what is it..and what do I do with it? Hmmmmmmm.