Web 2.0 refers to second generation of web-based services such as social networking sites, wikis, communication tools, and folksonomies that emphasize online collaboration and sharing among users. Millions of people are using Web 2.0 applications  such as Wikipedia or MySpace.

Though the term suggests a new version of the Web, it does not refer to an update to Internet or World Wide Web technical standards, but to fundamental shifts in how those standards are used. Because of this some technology-focused experts, notably Tim Berners-Lee, have questioned whether the term is meaningful.

Web 2.0 is the business revolution in the computer industry caused by the move to the internet as platform, and an attempt to understand the rules for success on that new platform.

A Web 2.0 website may typically feature a number of the following techniques:

• Rich Internet application techniques, optionally Ajax-based
• CSS
• Semantically valid XHTML markup and the use of Microformats
• Syndication and aggregation of data in RSS/Atom
• Clean and meaningful URLs
• Extensive use of folksonomies (in the form of tags or tagclouds, for example)
• Use of wiki software either completely or partially (where partial use may grow to become the complete platform for the site)
• Weblog publishing
• Mashups
• REST or XML Webservice APIs

Now check your website for these features and find whether you are using web 2.0 tools and techniques or not.

 source :: Wikipedia.org