What You Need to Know About Open Graph Meta Tags for Total Facebook and Twitter Mastery
It promotes integration between Facebook and other websites by allowing them to become rich graph objects with the same functionality as other Facebook objects.
It serves a similar purpose as the traditional meta title tag in your code. In fact, if Facebook doesn't find the og:title tag on your page, it uses the meta title instead. ... This meta data descriptor is very similar to the meta description tag in HTML.