The Tweet Button is a small widget which allows visitors to share content and connect on Twitter.
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.
A web page. Every web page is implicitly assumed to be declared to be of type WebPage, so the various properties about that webpage, such as breadcrumb may be used. We recommend explicit declaration if these properties are specified, but if they are found outside of an itemscope, they will be assumed to be about the page
A scheme.org entity that represents an organization such as a school, NGO, corporation, club, etc.
A scheme.org entity that represents an article, such as a news article or piece of investigative report. Newspapers and magazines have articles of many different types and this is intended to cover them all.
Sites who has this tag are verfied by google to use WebMaster tools