GraphQL is an open-source query language for APIs and a runtime for executing those queries with your existing data. Developed by Facebook, GraphQL enables clients to request exactly the data they need, reducing over-fetching and under-fetching of information. Unlike REST APIs, where endpoints return fixed data structures, GraphQL allows clients to specify the shape and structure of the response. This flexibility improves efficiency and performance, especially in complex applications. However, improper implementation can introduce security risks, such as data exposure or denial-of-service attacks, so strong authentication, authorization, and query validation are essential when using GraphQL in cybersecurity contexts.