This is a direct extract from the following link, a very well know and perhaps over used example of web2.0: http://en.wikipedia.org/wiki/Web_2#Characteristics_of_Web_2.0
While interested parties continue to debate the definition of a Web 2.0 application, a Web 2.0 web-site may exhibit some basic characteristics. These might include:
* “Network as platform” — delivering (and allowing users to use) applications entirely through a browser. See also Web operating system.
* Users owning the data on the site and exercising control over that data.
* An architecture of participation and democracy that encourages users to add value to the application as they use it.
* A rich, interactive, user-friendly interface based on Ajax or similar frameworks.
* Some social-networking aspects.
The concept of Web-as-participation-platform captures many of these characteristics.
Bart Decrem, founder and former CEO of Flock calls Web 2.0 the “participatory Web. ”