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.
Open graph description entity tag
The average rating based on multiple ratings or reviews.
Any offered product or service. For example: a pair of shoes; a concert ticket; the rental of a car; a haircut; or an episode of a TV show streamed online.
A review of an item - for example, of a restaurant, movie, or store.
Sites who has this tag are verfied by google to use WebMaster tools