See what your Facebook friends have liked, shared, or commented on across the Web. This includes all variations of Like, Share and Follow Buttons, Embedded Posts, Comments, Activity Feed, Recommendations Feed, Recommendations Bar, Like Box and Facepile.
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
Meta descriptions are HTML attributes that provide concise explanations of the contents of web pages. Meta descriptions are commonly used on search engine result pages (SERPs) to display preview snippets for a given page.
Sites who has this tag are verfied by google to use WebMaster tools
A canonical link element is an HTML element that helps webmasters prevent duplicate content issues by specifying the "canonical", or "preferred".