Web 2.0 was coined as a cool name for a conference about the state of the internet back in 2004. Kind of a play on the fact that software is released in ‘versions’ (1.1, 1.4, 1.2.3.1.2, etc, etc) whereas the web is clearly evolving and branching in a way that defies this kind of classification.
Web 2.0 draws an arbitrary line that says the current state of the web is significantly different now from how it was a few years ago.
There’s been a lot of talk about what Web 2.0 really means and what it doesn’t (here’s the official line from Tim O’Reilly who coined the term).
Here’s an anthropological take on Web 2.0:

