Web 2.0 is not a new software but a new way of using the Internet. In the simplest form it refers to user created content. Here is more plucked form Wikipedia (Wikipedia is a classic web 2.0 application):
Web 2.0 websites allow users to do more than just retrieve information. They can build on the interactive facilities of “Web 1.0” to provide “Network as platform” computing, allowing users to run software-applications entirely through a browser. Users can own the data on a Web 2.0 site and exercise control over that data. These sites may have an “Architecture of participation” that encourages users to add value to the application as they use it. This stands in contrast to traditional websites, the sort that limited visitors to viewing and whose content only the site’s owner could modify.
Dental web 2.0 applications are, Dental Practice Optimizer, Demand Force, PLZ, Sesame, ddsWeblink. and more.