Here read this:
http://webtrends.about.com/od/web20/a/what-is-web-30.htm
and this about 2.0
http://en.wikipedia.org/wiki/Web_2.0
I believe web 3.0 has been around for a couple of years (don't take my word for it)
BTW... this was a ridiculously easy question to google... or at least search this forum...