Web 2.0 is a term which refers to the new face of the internet that fosters user participation and action via social media, blogs, community, wikis, audio and video sharing sites, photo sharing sites, interactive web based tools, mashups and much more.
Although the term Web 2.0 was first used by Darcy DiNucci in the year 1999, it was made popular by Tim O'Reilly through his O'Reilly Media Web 2.0 conference.
While the term Web 2.0 now signifies just about any social aspect of the web where the user is given importance, there are people who don't agree on what exactly Web 2.0 should mean.
Inspite of all the disagreements, it's evident that the evolution of internet after the dot-com bubble burst in 2000-01 has led to a complete change in the way websites and communities operate. The end user is the focus now and what he says is diligently heard. I guess that is what Web 2.0 is all about.
Image Credit - Alvy.