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
Sites who has this tag are verfied by google to use WebMaster tools
When running in a browser on a mobile phone, "format-detection" meta tag determines whether or not telephone numbers in the HTML content will appear as hypertext links. The user can click a link with a telephone number to initiate a phone call to that phone number.
A canonical link element is an HTML element that helps webmasters prevent duplicate content issues by specifying the "canonical", or "preferred".