Open Graph Protocol
- "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 allow any web page to have the same functionality as any other object on Facebook."
- "While many different technologies and schemas exist and could be combined together, there isn't a single technology which provides enough information to richly represent any web page within the social graph. The Open Graph protocol builds on these existing technologies and gives developers one thing to implement. Developer simplicity is a key goal of the Open Graph protocol which has informed many of the technical design decisions."
The open graph protocol is a standard for metadata to show previews of websites. Spearheaded by Facebook, it's an open standard that allows anyone to configure previews of images, videos, or other content from a website.
Twitter has their own approach, and Facebook has their own Facebook-specific previews as well, but the open protocol is what most websites use and/or will fall back to to display the site.