Quantcast helps advertisers and publishers better understand, find and access targeted audiences in real-time. Marketers use Quantcast to amplify their targeting and reach consumers who look just like their best performing customers with unprecedented performance and scale. Publishers use Quantcast to directly measure and packag...
The Tweet Button is a small widget which allows visitors to share content and connect on Twitter.
Facebook's Like button is the quickest way for people to share content with their friends. A single click on the Like button will 'like' pieces of content on the web and share them on Facebook. You can also display a Share button next to the Like button to let people add a personal message and customize who they share with.
Open graph description entity tag
Sites who has this tag are verfied by google to use WebMaster tools