The term Web 2.0 is used to describe a perceived second generation of web development and design.
The first Generation of the Web was largely focused on connecting people to information. The second generation Web 2.0 was developed to facilitate communication between people.
Web 2.0 allows more than just the receiving of information; users can interact with these websites, commenting on information they find and building sites and resources to further increase the information available.
Some popular web 2.0 sites include:
Facebook, YouTube, Campfire, Flickr, Slide, Blogger, Digg, Delicious, Stumble upon, Skype, Wikipedia, Feed Burner, Ecademy and LinkedIn.
Web 2.0 has changed the way people use the Internet and opened up many avenues through which you can market your website online.
It is very important that you do not spam social sites; their users will turn on you, which will result in bad publicity for your website.