Apps that link to your content can then use this metadata to deep-link into your app, take users to an app store to download the app, or take them directly to the web to view the content.
PHP is a widely-used general-purpose scripting language that is especially suited for Web development and can be embedded into HTML.
Open graph description entity tag
The average rating based on multiple ratings or reviews.
Sites who has this tag are verfied by google to use WebMaster tools