Facebook is an online social networking service whose name stems from the colloquial name for the book given to students at the start of the academic year by some university administrations in the US to help students get to know each other. It was founded in February 2004 by Mark Zuckerberg with his college roommates and fellow Harvard University students Eduardo Saverin, Andrew McCollum, Dustin Moskovitz and Chris Hughes.
Users must register before using the site, after which they may create a personal profile, add other users as friends, and exchange messages, including automatic notifications when they update their profile. Aditionaly, users may join common-interest user groups, organized by workplace, school or college, or other characteristics, and categorize their friends into lists. At S
eptember 2012, Facebook has over one billion active users. Facebook has affected the social live and the acticity of people in various ways. With its availability on mobile devices, Facebook allow users to continiously stay in touch with friends. It can also unite people with common interests or beliefs through groups and pages, and has been known to reunite lost family members and friends because of the widespread reach of its network.