GraphQL is a query language for APIs. Its purpose is to provide a complete description of the data in your API, which can then be used by clients to ask for specific data from the API. A GraphQL query is a string that is sent to a server to be interpreted and fulfilled, which then returns JSON back to the client. The developers differentiate the way GraphQL works as handling data not in terms of resource URLs, secondary keys, or join tables; rather as a graph of objects and the models ultimately used in apps like NSObjects or JSON.
http://www.i-programmer.info/news/90-tools/10095-graphql-leaves-tech-preview.html