GraphQL is a query language for APIs and a runtime for fulfilling those queries with your existing data, as it 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.
The main advantage of GraphQl over REST is that REST responses contain too much data or sometimes not enough data, which creates the need for another request. GraphQL solves this problem by fetching only the exact and specific data in a single request.
GraphQL is an application layer server-side technology that is used for executing queries with existing data while REST is a software architectural style that defines a set of constraints for creating Web services. GraphQL can be organized in terms of a schema whereas REST can be arranged in terms of endpoints.
GraphQL allows making multiple resources request in a single query call, which saves a lot of time and bandwidth by reducing the number of network round trips to the server. It also helps to save waterfall network requests, where you need to resolve dependent resources on previous requests.