Facebook is a social networking service launched in February 2004, owned and operated by Facebook, Inc.As of June 2012, Facebook has over 955 million active users, more than half of them using Facebook on a mobile device. 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. 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". The name of the service stems from the colloquial name for the book given to students at the start of the academic year by some university administrations in the United States to help students get to know each other.