It's hard to get your arms around the quickly evolving language of the Internet. Eric Reyes has a great article in the May/June 2007 issue of Revenue Magazine that does a good job of defining Web 2.0. He quotes Tim O'Reilly, the person that coined 2.0.
"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."
The article goes on to define the key phrases associated with Web 2.0:
Ajax - Programming language that allows you to refresh a part of a web page instead of the entire page.
Mashup - When the functionality of two web pages combine into one experience.
Mobile Web - Accessing the Internet from any mobile device.
Podcast - An audio file that mimics a radio broadcast and is made available over the web.
RSS Feed - Internet content you can subscribe to and that is "pushed" to your computer.
Social Bookmarking - The storage of your favorite sites on the web in a place where others can access them when looking for similar experiences or content.
User-generated content - Content created or influenced by visitors to a web site.
Web 2.0 - An Internet experience that is collaborative or interactive.
Widget - A program within a program such as a box that contains a weather report.
Wiki - A site where visitors can edit and add content.
Just when you get this language down, along comes Web 3.0 where the web uses artificial intelligence to adapt the experience to you. Instead of search you will find. I hope so, because finding out what all this means is a full time job. I'm sure by the time you read this we'll be up to 4.0.