Walls are an important part of it

• Popular surfers' hangout
• Zuckerberg's company
• One of dozens, for millions
• Social networking service with over a billion active users
• Place to befriend or be friended
• MySpace alternative
• Social media website

Wiktionary Word definitions in Wiktionary
n. 1 A reference book or electronic directory made up of individuals’ photographs and names. 2 A college publication distributed at the start of the academic year by university administrations with the intention of helping students get to know each other ...

Douglas Harper's Etymology Dictionary Word definitions in Douglas Harper's Etymology Dictionary
directory listing names and headshots, by 1983, originally among U.S. college students, from face (n.) + book (n.). The social networking Web site of that name (with capital F- ) dates from 2004.