Social networking sites are websites or web-based services which allow people to create online communities. These communities may be based on shared characteristics such as interests, geographical location, or attendance at the same educational institution.
In general, social networking sites require you to register and create an account before using them. Services on these sites are often free.
Familiar examples of social networking sites include Facebook, My Space, and Twitter.
Twitter is a service for friends, family, and co–workers to communicate and stay connected through the exchange of quick, frequent messages. People write short updates, often called "Tweets" of 140 characters or fewer. These messages are posted to your profile or your blog, sent to your followers, and are searchable on Twitter search.