Open Graph tags are code (technically, ‘meta tags’) that are added to your website to describe key aspects of your site – things like the title, the description and the main image.
Developed by Facebook (but now adopted widely), the Open Graph protocol’s real value is that by explicitly specifying your site’s key elements, you gain control over how Facebook displays your site when you post links to it on Facebook.
Without Open Graph tags, Facebook makes a best guess at what the link to your site should be. In many cases this might be perfect. But there will be times when Facebook will use an image that isn’t the best one, or it might pull a description from the page that’s too long.
By using OG you get a big say in how the post is formatted on Facebook, and that in turn helps shape the decision by someone to click that link. So you can begin to see the real value of using OG tags, especially if you are using posts to link to your site to drive business.
OG tags come in many shapes and sizes. You can usually define them in your CMS like WordPress.
There are dozens of OG tags, but the main ones are OG:title and OG:description, which let you specify the title and description of your site. OG:image is another important one, since it lets you specify which image Facebook uses in the link. For a full list of OG tags see http://ogp.me/, and for how Facebook uses them read https://developers.facebook.com/docs/sharing/webmasters
It’s a good habit to think about your OG tags, since it’s not just Facebook that uses them. Twitter will make use of any OG tags, but have their own set of similar tags so you can fine-tune your post links in Twitter.
Just as meta tags help control how search engines display your site in search results, OG Tags help you gain some control over your posts on social platforms. Use them!