In 2007 Mark Zuckerberg introduced the concept of the social graph, a map of all the ways Facebook users are connected to one another.
Three years later, on April 21, 2010, Zuckerberg revealed his plans for the Open Graph protocol, which would let users connect Facebook to other apps and services. For the first time, Facebook users could share their activity on the Web -- beyond the walls of Facebook.
But Zuckerberg's vision has either proved annoying (bombarding you with everyone's Spotify activity), embarrassing (revealing that terrible movie you watched on Netflix(NFLX)), or invasive (broadcasting every news story you read on the Internet). Facebook later scaled back its use of open graph data.
But last year, Facebook introduced Graph Search, a tool that lets users access the graph themselves and search for the data they want. For example, you could search for any photos that two specific friends commented on. Eventually you will be able to conduct highly-detailed, contextual searches in every corner of Facebook, discovering which of your friends shared a song from Drake in September of 2009, or who has given good reviews to a certain restaurant.