The Open Graph protocol enables any web page to become a rich object in a social graph. For instance, this is used on Facebook to enable any web page to have the same functionality as a Facebook Page. @en
(2013-05-30) Ghislain Atemezing: The Open Graph Protocol made by Facebook to richly represent any web page within the social graph, with a minimum set of four metadata (og:title, og:type, og:image, og:uri). Note that this vocabulary only contains properties.