Web 2.0 is defined as an intersection of web application features that facilitate participatory information sharing, interoperability, user-centered design, and collaboration on the World Wide Web. A Web 2.0 site allows users to interact and collaborate with each other in a social media dialogue as creators (procurers) of user-generated content in a practical society, in contrast to websites where users (consumers) are limited to the passive viewing of content that was created for them. Even though the term suggests a new version of the World Wide Web, it is not an update to any technical specification, but rather a drastic change in the ways software developers and end-users use the Web.
This is basically a system that breaks with the old model of centralized Web sites and moves the power of the Web/Internet to the desktop.
Web 2.0 websites allow users to do more than just retrieve information; they provide the user with more user-interface, software and storage facilities, all through their browser. The Web 2.0 offers all users the same freedom to contribute.