Web 2.0: 1. a term that refers to a supposed second generation of Internet-based services. These usually include tools that let people collaborate and share information online, such as social networking sites and wikis. 2. a term to generally describe web sites and services where the content is shaped partially or entirely by the users, instead of being read-only. - google.com Definitions
Web 2.0 is a trend in the use of World Wide Web technology and web design that aims to facilitate creativity, information sharing, and, most notably, collaboration among users.
A term often applied to a perceived ongoing transition of the World Wide Web from a collection of websites to a full-fledged computing platform serving web applications to end users.
Web 2.0 term was first coined by Tim O'Reilly . It refers to the new trend in web. its all about communities, blogging, social networking. Sites having Ajax, fancy widgets, effects are also called web 2.0 powered.