Web 2.0 was referred as the idea of the "Web as a platform". It allowed the readers to actually interact with the Web pages more like you would with an application on your desktop. Some application that is a form of Web 2.0. are Google maps, Digg, Gmail and so on.
Examples of Web 2.0 include social networking sites, blogs, wikis, video sharing sites.. read more- http://en.wikipedia.org/wiki/Web_2.0