What is Web 2.0?

In layman’s terms, Web 1 was mostly static, pages didn’t change that often, and there was not much interactivity between the website and its visitors. Webmasters controlled access to the web content and changes had to go through them.

Web 2 is more dynamic and interactive. New software makes it easier for anyone to add and modify content. Successful websites build communities of like-minded individuals to build traffic to their site. There is more digital media, both photos and video. People can use software situated on the web at low cost instead of installing it on their own computer. Web 2 refers to the evolving web which makes use of better software and more bandwidth.

Here is the definition from Wikipedia:
Web 2.0 is a term popularized by O’Reilly Media and MediaLive International as the name for a series of web development conferences that started in October 2004. It has since come to refer to what some people describe as a second phase of architecture and application development for the World Wide Web.

Web 2.0 applications often use a combination of techniques devised in the late 1990s, including public web service APIs (dating from 1998), Ajax (1998), and web syndication (1997). They often also allow for mass publishing (web-based social software), so the term may include blogs and wikis. To some extent Web 2.0 has become a buzzword, incorporating whatever is newly popular on the Web (such as tags and podcasts), so that a consensus on its exact meaning has not yet been reached.