A social network is a social structure that facilitate a communication among each individual or organization where connected by one or more a specific interdependence, same interest, same ideas, or to share information and doing friendship.

A social network is a social structure, community, or society made of nodes which are generally accounts, individuals or organizations. It indicates the ways in which they are connected through various social familiarities, affiliations and / or relationships ranging from casual acquaintance to close familial bonds. (Hendrik Speck, 2007)

The social network can be visualize as the following.

Social network explain the relationship between one user to other in terms of common interests, common status, or common background. Social network also used as tool to promote user, to create personal branding until doing theirs own business.

Social network concept allows users to have a repository in the term of text, image or video that can be accessed and commented by their friends

Facebook, Twitter, MySpace are the famous social network website. 

Facebook is developed in Februari 2004 by Mark Zuckerberg and assisted by Dustin Moskovits, Chris Hughesan and two Harvard students. Facebook has social network concept, and the biggest 10 sites in the world based on research from Alexa. This social network concept used to improve the number of users. 

Facebook could be accessed by people in September 2006. One year later, Facebook has 42 million users around the world. Now more than 300 million users registered around the world. According to Alexa, Facebook in the 1st rank in Indonesia. 

O'Reilly Research also provide some information about active facebook user by country and region by August 2009.

..to be continued..