Open Graph content
When you insert a link into an email, or a post on Facebook, Twitter, LinkedIn, etc,. have you noticed how many of these links cause an image and decriptive content to appear just below that link?
This doesn't happen just like that
but is the result of that specific web page containg open graph tags.
Facebook, Twitter, LinkedIn, etc., have slightly diffent methods, but essentially each one will be looking for correctly formatted OG tags
containing headline content, a description and an image to display.
Unless you were to view the source code of a web page, you wouldn't be able to see these open graph tags because they're embedded into the page code, but you can probably see the benefit of having a visual and informative way of displaying information about that link to anyone who views your post or email.
By default, if you select the Open Graph content
option, the website calculator will work out a price based on the number of pages you selected. You might decide that you only want OG tags on specific pages, but this detail can be discussed prior to your website being built, and of course the price will be reduced accordingly.