Many definitions of Web 2.0 are floating around. I answered what is Web 2.0 on Scriptalicious recently as such:
Web 2.0 refers to the second and latest major phase of evolution for the World Wide Web. It encapsulates a general shift to newer, more socially and technologically evolved Websites and Web services.Quite common now, Tim O'Reilly gives us a pretty comprehensive look at the origins of the term, and the various concepts and technologies it expresses. However, no clear definition can be derived from most of this and tons of people still argue about it's tangibility. When Tim posted the original "What is Web 2.0" article in September of 2005, he states that there are approximately 9.5 million citations in Google searching for the terms Web 2.0. A Google search for Web 2.0 now returns 329,000,000 results. That's almost 34 times as many results as there were less than four years ago.
Since the phrase Web 2.0 was introduced before a clear definition was even formulated, it has led to wild debate. This is okay, though. Despite personal opinion and interpretion, it seems that most Web professionals agree upon one common definition:
Web 2.0 represents an evolutionary shift in how the Web works.Perhaps everyone won't agree with me on this. But the common trend among everyone's definition of what Web 2.0 is describes an evolving Web. The bubble bursting forced the strong to be stronger, and shoved the weak out of the game entirely. What's left is the Web that evolved to meet the challenges of a lucrative yet harsh user-centric world.