Facebook, the social media platform founded by Mark Zuckerberg, is named after the physical dormitory directories or "face books" that contained pictures of people at Harvard University.
After being jilted by a girl, Zuckerberg developed a controversial site called FaceMash that encouraged students to vote on the attractiveness of their peers, even mentioning the term facebook several times in a blog posted while developing it:
"The Kirkland facebook is open on my desktop and some of these people have pretty horrendous facebook pics. I almost want to put some of these faces next to pictures of farm animals and have people vote on which is more attractive.”
He was reprimanded by the Administrative Board after complaints but undeterred went on to create a new site in February 2004 that enabled Harvard students to connect with one another - he called it The Facebook (www.thefacebook.com).
Just 18 months later, after the site had hit one million users, the company rebranded with Zuckerberg paying $200,000 for the www.facebook.com domain so they could drop the 'the' from their name. There are suggestions this had always been the intention, they just need to raise the capital to buy the name.
Sources: FaceMash creator survives ad board | Why is Facebook called Facebook