GraphQL is a query language for APIs and a runtime for fulfilling those queries with your existing data. GraphQL provides a complete and understandable description of the data in your API, gives clients the power to ask for exactly what they need and nothing more, makes it easier to evolve APIs over time, and enables powerful developer tools.
A headless Content Management System, or headless CMS, is a back end-only web content management system that acts primarily as a content repository. A headless CMS makes content accessible via an API for display on any device, without a built-in front end or presentation layer. The term ‘headless’ comes from the concept of chopping the ‘head’ (the front end) off the ‘body’ (the back end).