GraphQL is an open-source data query and manipulation language for APIs and a runtime for executing those queries with existing data. It was developed by Facebook and is used extensively for building client applications. GraphQL provides a flexible, efficient, and type-safe alternative to traditional REST APIs. It allows clients to specify the exact data they need in a single request, reducing over-fetching and under-fetching of data. GraphQL's schema-based approach enables introspection and auto-generation of documentation, making it easy for developers to understand and work with APIs. It supports real-time updates, data aggregation, and complex data relationships, making it suitable for building dynamic and interactive applications. GraphQL is used by companies such as Facebook, GitHub, Twitter, and Shopify to power their APIs and improve developer productivity and user experience.