What are the characteristics of "Web 2.0"?

I've been hearing the buzzword "Web 2.0" around certain circles.  What is that exactly?  Is that a style of "look-and-feel" for website designs?  If so, what are its characteristics of "Web 2.0"?

try this http://www.google.com/search?hl=en&q=web+2.0&btnG=Google+Search

Web 2 is a lot of things that describe the new style of web sites like digg, flickr, etc.

very technical term but can be dismissed as a buzzword... Generally it pertains now to certain design styles popularized by blogger, flickr etc... now even others use these to term AJAX type or powered sites... So it generally is a label of the current trend in design and online softwares...

Hehe, this is maybe the best definition I heared for web 2.0

Anyway it seems that web 2.0 is not meaning something specific, but it is more like a marketing phrase.

Web 2 is the new technologies for the web. Which is generally AJAX, therefore the pages would load much faster and you don't need to press "back" bottom on your browser.