A pingback is one of four types of linkback methods for Web authors to request notification when somebody links to one of their documents. This enables authors to keep track of who is linking to, or referring to their articles.
Facebook Connect allow users to connect their Facebook identity, friends and, privacy to any website. Facebook Connect is Facebook's first attempt to allow access to Facebook user data outside of Facebook itself. The company is describing it as giving third party applications access to much of the same data as Facebook applicat...
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
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".