Facebook (stylized facebook) is a social network service and website launched in February 2004 that is operated and privately owned by Facebook, Inc. As of January 2011, Facebook has more than 600 million active users. Users may create a personal profile, add other users as friends and exchange messages, including automatic notifications when they update their profile. Additionally, users may join common interest user groups, organized by workplace, school, or college, or other characteristics. The name of the service stems from the colloquial name for the book given to students at the start of the academic year by university administrations in the US with the intention of helping students to get to know each other better.
Facebook was founded by Mark Zuckerberg with his college roommates and fellow computer science students Eduardo Saverin, Dustin Moskovitz and Chris Hughes. The website's membership was initially limited by the founders to Harvard students, but was expanded to other colleges in the Boston area, the Ivy League, and Stanford University. It gradually added support for students at various other universities before opening to high school students, and, finally, to anyone aged 13 and over.