This document provides a summary of Facebook in 3 sentences: Facebook is a social networking site with over 200 million users that allows users to create profiles, connect with friends, share photos and updates, and engage with groups and applications. The document outlines the basic functions of Facebook including profiles, friending, posting updates and links, using applications, and accessing Facebook through websites and mobile devices. It also discusses potential risks of using Facebook and losing privacy if one's profile is accessed unexpectedly or through bugs in the system.