A family of standard web feed formats used to publish frequently updated information like blog entries, news headlines, audio and video.
Open graph description entity tag
The Open Graph protocol enables any web page to become a rich object in a social graph, a open protocol supported by Facebook
A WebSite is a set of related web pages and other items typically served from a single web domain and accessible via URLs.
Sites who has this tag are verfied by google to use WebMaster tools