What are Open Graph meta tags?

vidr.io doesn’t have any Open Graph tags. I didn’t know what Open Graph was until yesterday. It’s a standard which defines some <meta> tags describing a webpage. Those tags are intended to be used when embedding the page elsewhere, such as when the URL is shared in social media.

Open Graph meta tags all take the form: <meta property="og:KEY" content="VALUE"/>. Open Graph has four “required” keys: title, type, image and url. The type is one of a set of strings like website, video, music, profile, etc., and depending on the type, there are more properties you can define.

The other required properties seem to have equivalents in pre-existing tags: