Web 2.0 and Web 3.0 are terms that refer to the trends and characteristics believed to be representative of next generation web applications emerging after the dot-com collapse of 2001. The term Web 2.0 became widely used after the first O’Reilly Media Web 2.0 Conference (http://www.web2con.com/) in 2004.
Active participation, collaboration, and the wisdom of crowds. Consumers explicitly improve and add value to the web application they are using either through volunteerism or in response to incentives and rewards. This typically involves explicitly creating and modifying content (Wikipedia entries, Amazon reviews, Flickr tags, YouTube videos, etc.)