What is Web 2.0? A simple explanation

There is a buzzword called web 2.0 going around the web recently. So what the heck is Web 2.0?

Wikipedia which itself a web 2.0 site says..."Web 2.0, a phrase coined by O'Reilly Media in 2004, refers to a supposed second-generation of Internet-based services — such as social networking sites, wikis, communication tools, and folksonomies — that let people collaborate and share information online in previously unavailable ways."

I found the most simple explanation of the buzzword on the following Informationweek article.

link: The skinny on web 2.0