What is Web 2.0? Few terms today are used so often with so little understanding or agreement as to a precise definition as Web 2.0.
In very general terms, Web 2.0 refers to a new generation of websites and related technologies that are significantly smarter and more interactive than 1999-era sites. Web 2.0 sites tend to be more user-focused, and may allow user-created content to be used on the site. One simple comparison often used to illustrate the difference between Web 2.0 and Web 1.0 (another invented term applied to older web technology after the fact) is Encyclopedia Brittanica vs. Wikipedia.com. The former is traditional, static web content created by a small group of authors and editors; the latter is a dynamic community site with many thousands of members adding and revising content.
Blogs, which allow visitors to interact with the site author(s), are often cited as a Web 2.0 phenomenon.
In general, sites that allow social networking are considered to be Web 2.0, as are sites that use web services to exchange data.
One of the better explanations of Web 2.0 is O'Reilly's lengthy blog post on the subject. While everyone may not agree on O'Reilly's definition and characterization of Web 2.0, it's a very good starting point. Wikipedia also has a Web 2.0 entry of significant depth.
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