Web 2.0

Definition:

Web 2.0, a relatively new term used to define what is fast becoming the new World Wide Web (WWW) of today.

Web 2.0 is not a new type of WWW, speaking from a technical point of view, nothing tech or spec related has changed from Web 1.0, but 2.0 is used to define the new ways in which the web is being used.
This new way, fast becoming increasingly popular, mostly differs from Web 1.0 by the level of interactivity online. For example, the users are able to more directly influence, change, edit information online. Be this in the form of a weblog (blog), image sharing, forums etc.

Web 2.0 isn't only for personal use, the professional possibilities for such interactivity are also highly beneficial. Software such as Skype for example, allows users to speak with others anywhere in the world, and even host conference calls in the same way.

Examples:

Blogger - WebLogs for users, very easy to use and maintain.
Wikipedia - Information sharing on a worldwide level, entered and edited completely by users.
Flickr - Image sharing, simple to use and to share to anyone online.