Web 2.0 is an term referring to the ongoing transition to a full participatory Web, with participation including both humans and machines. Web 2.0 is characterized by the following themes:
The Read/Write Web: In which the Web is seen as a two-way medium, where people are both readers and writers. The main catalyst for this is social software, allowing communication and collaboration between two or more people.
The Web as Platform: In which the Web is seen as a programming platform upon which developers create software applications. The main catalyst for this is Application Programming Interfaces, or APIs, allowing communication between two or more software applications.
It is important to recognize, however, that “Web 2.0” is not anything other than the evolving Web as it exists today. It is the same Web that we’ve had all along. But the problems, issues, and technologies we’re dealing with are in many ways different, and so using the term “Web 2.0” is a recognition that the Web is in a constant state of change, and that we have entered a new era of networked participation.