Facebook introduced Open Graph in 2010. It promotes integration between Facebook and other websites by allowing them to become rich “graph” objects with the same functionality as other Facebook objects. The Open Graph protocol was originally created at Facebook and is inspired by Dublin Core, link-rel canonical, Microformats, and RDFa.
Put simply, a degree of control is possible over how information travels from a third-party website to Facebook when a page is shared (or liked, etc.). In order to make this possible, information is sent via Open Graph meta tags in the <head> part of the website’s code.
Now, other social media sites also are taking advantage of social meta tags. All of the other major platforms, Twitter, LinkedIn, and Google+, recognize Open Graph tags. Twitter actually has its own meta tags for Twitter Cards, but if Twitter robots cannot find any, Twitter uses Open Graph tags instead.