One year ago Tim O’Reilly published the long article What is Web 2.0 that lists examples of Web 2.0 applications and services. The problem is that this document is very long and is not really a definition. The good news is that Tim O’Reilly, just published a compact definition of Web 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. Chief among those rules is this: Build applications that harness network effects to get better the more people use them.