There is a huge amount of disagreement of what Web 2.0 means. Out of eight definitions (I am sure there are more!), I found the definition and explantion from O’Reilly quite interesting.
Instead of explaining Web 2.0 here, I would provide some examples of Web 2.0 softwares, Yahoo! Maps, Google Maps, MSN Maps, LinkedIn. You can find a detailed list at http://web2.wsj2.com/more_great_web_20_software.htm. In my opinion, for better or for worse this term “Web 2.0” is here to stay.