Open Graph tagging is a system that Facebook uses to determine what you would like posted to their platform.
If you have an item that you would like posted to Facebook, Facebook will generally "scrape" the content for images, title, and description so that they can post more than just a link to your Facebook page.
In essence, Open Graph is a tagging system that can be implemented in page metadata to customize what Facebook finds for images, title, and description data.
What should I include in my Open Graph tags?
Typically, the basic tags should include og:title, og:image, og:type, and og:url. You can add description content if you wish to have a specific summary included with your article.
For example, a basic Open Graph markup should look like this:
For more detailed Open Graph tag options, take a look at http://ogp.me/.