LinkedIn Plugins are a way to drop LinkedIn functionality into websites.
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Google+ platform websites integration using the Google+ platform tag.
The Tweet Button is a small widget which allows visitors to share content and connect on Twitter.
Let visitors recommend your content on Google Search and share it on Google+.
Pinterest is a social networking site with a visually-pleasing virtual pinboard interface. Users collect photos and link to products they love, creating their own pinboards and following the pinboards of other people whom they find interesting. The site has experienced rapid growth in recent months.
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.
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".