Facebook is an online social networking service. Its name comes from a colloquialism for the directory given to American university students. Facebook 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. The founders had initially limited the website's membership to Harvard students, but later expanded it to colleges in the Boston area, the Ivy League, and Stanford University. It gradually added support for students at various other universities before it opened to high-school students, and eventually to anyone aged 13 and over. Facebook now allows anyone who claims to be at least 13 years old to become a registered user of the website.
Users must register before using the site, after which they may create a personal profile, add other users as friends, exchange messages, and receive automatic notifications when they update their profile. Additionally, users may join common-interest user groups, organized by workplace, school or college, or other characteristics, and categorize their friends into lists such as "People From Work" or "Close Friends". As of September 2012, Facebook has over one billion active users, of which 8.7% are fake. Facebook (as of 2012) has about 180 petabytes of data per year and grows by over half a petabyte every 24 hours.
In May 2005, Accel partners invested $12.7 million in Facebook, and Jim Breyer added $1 million of his own money. A January 2009 Compete.com study ranked Facebook the most used social networking service by worldwide monthly active users. Entertainment Weekly included the site on its end-of-the-decade "best-of" list, saying, "How on earth did we stalk our exes, remember our co-workers' birthdays, bug our friends, and play a rousing game of Scrabulous before Facebook?" Facebook eventually filed for an initial public offering on February 1, 2012; it is headquartered in Menlo Park, California.[2] Facebook Inc. began selling stock to the public and trading on the NASDAQ on May 18, 2012. Based on its 2012 income of US$5.1 billion, Facebook joined the Fortune 500 list for the first time on the list published in May 2013, being placed at position 462.

Type:    Public
Traded as:    NASDAQ: FB 
Foundation date:    Cambridge, Massachusetts, U.S. (February 4, 2004)
Headquarters:    Menlo Park, California, U.S.
Area served:    United States (2004–05), Worldwide (2005–present)
Mark Zuckerberg
Eduardo Saverin
Andrew McCollum
Dustin Moskovitz
Chris Hughes
Key people:    Mark Zuckerberg (Chairman and CEO), Sheryl Sandberg (COO)
Industry:    Internet
Revenue:    Increase $5.1 billion (2012)
Operating income:    Decrease US$ 538 million (2012)
Net income:    Increase US$ 53 million (2012)
Total assets:    Increase US$ 15.10 billion (2012)
Total equity:    Increase US$ 11.75 billion (2012)
Employees:    5,794 (September 2013)
Subsidiaries:    Instagram
Website:    facebook.com
Written in:    C++ and PHP
Alexa rank:    Steady 2 (December 2013)
Type of site:    Social networking service
Registration:    Required
Users:    1.19 billion (active September 2013)
Available in:    Multilingual (70)
Launched:    February 4, 2004