GraphQL is a modern query language for APIs and a server-side runtime for executing those queries using your existing data. Unlike traditional REST APIs that expose multiple, rigid endpoints, GraphQL provides a single endpoint where clients can send a query specifying the exact data fields they need, including data from related resources. This client-driven approach eliminates the common problems of over-fetching (receiving more data than needed) and under-fetching (requiring multiple API calls to gather all necessary data), leading to more efficient and flexible communication between the client and server. The entire system is governed by a strongly-typed schema, which defines the API's capabilities and serves as a contract, enabling powerful developer tools and introspection.