The dividing line between Web 1.0 and 2.0 was, roughly speaking, the dotcom crash. In terms of business model, Web 2.0 is the era of Freemium and User Generated Content, and of Google Adwords. One of the original poster children for this was Flickr, another was Blogger.

Technologically, there isn't much to separate the eras, except perhaps the deprecation of Big Iron approaches to infrastructure in favor of horizontal scaling with commodity hardware, but that's really a spectrum rather than a sharp division.

The Web 2.0 era really hasn't ended, regardless of how the web and it's infrastructure has evolved in the past 20 years. There are various candidates for what will define the next era, but so far none that are indisputably "it".