this question begs the question that yedda should first submit all questions to wikipedia before validation.. anyway:

http://en.wikipedia.org/wiki/Web_2.0

The phrase Web 2.0 was coined by O'Reilly Media to refer to a supposed second generation of Internet-based services that let people collaborate and share information online in a new way—such as social networking sites, wikis, communication tools, and folksonomies. O'Reilly Media, in collaboration with MediaLive International, used the phrase as a title for a series of conferences and since then it has become a popular, if ill-defined and often criticized, buzzword amongst the technical and marketing communities.