Today I got asked, what is Web 2.0, well there are various definitions available on the web.

From Wikipedia

In studying and/or promoting web-technology, the phrase Web 2.0 can refer to a trend in web design and development — a perceived second generation of web-based communities and hosted services (such as social-networking sites, wikis, blogs, and folksonomies) which aim to facilitate creativity, collaboration, and sharing between users.

From O’Reilly

Like many important concepts, Web 2.0 doesn’t have a hard boundary, but rather, a gravitational core. You can visualize Web 2.0 as a set of principles and practices that tie together a veritable solar system of sites that demonstrate some or all of those principles, at a varying distance from that core.

and

If Netscape was the standard bearer for Web 1.0, Google is most certainly the standard bearer for Web 2.0.

It can even be a picture.

However I think this video really sums it up.