The Graph API is the primary way to get data in and out of Facebook's platform. It's a low-level HTTP-based API that you can use to query data, post new stories, manage ads, upload photos and a variety of other tasks that an app might need to do.
The Graph API is named after the idea of a 'social graph' - a representation of the information on Facebook composed of:
The Graph API is HTTP based, so it works with any language that has an HTTP library, such as cURL, urllib. We'll explain a bit more about what you can do with this in the section below, but it means you can also use the Graph API directly in your browser, for example a Graph API request is equivalent to:
GET graph.facebook.com /facebook/picture? redirect=false