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+.
Open graph description entity tag
A WebSite is a set of related web pages and other items typically served from a single web domain and accessible via URLs.
Sites who has this tag are verfied by google to use WebMaster tools
By adding rel="home" to a hyperlink, a page indicates that the destination of that hyperlink is the homepage of the site in which the current page appears.