Web 2.0 refers to the second generation of the Web. However, this is not about launching a new Web service as such.
Web 2.0 is about the growth of interactive content and collaboration online, something that was not possible during the early days of the web in the 1990s.
Collaboration amongst internet users is in fact the biggest difference between Web 1.0 and Web 2.0.
While in the first version of the Web users were typically passive while viewing content on sites, in 2.0 there is a lot more interaction.