It's basically a site with a reflection logo and some sort of social interaction. Web 2.0 doesn't exist - it's a buzzword used by people in turtle necks and square glasses to squeeze money out of clients, and to generate hype from the general public about their new "web 2.0 social hub website blablabla".
No it's not. Here is some information. http://www.oreillynet.com/pub/a/oreilly/tim/news/2005/09/30/what-is-web-20.html Hope that helps mate.
Maybe you could buy the O'Reilly Web 2.0 PDF ebook for $375 USD and find out more? This has been discussed to death on DP, this thread has some particularly good posts (IMHO) on the subject: http://forums.digitalpoint.com/showthread.php?t=783594
As above it's just a term coined to describe the new-generation websites that are being published. Forgetting Web 2.0 as a web publisher you should ensure that at present Your sites have the ability to exchange data They have the ability to generate automatic content They have an efficent design, presentation is key but keeping loading time firmly in mind You can publish feeds Users can comment - or any user interaction Easily updatable