React Native is an open-source framework, created by Meta, that enables developers to build natively rendered mobile applications for iOS and Android using a single JavaScript codebase. It extends the React library, allowing developers to compose rich user interfaces from declarative, component-based building blocks written in JSX, which then directly translate to the platform's native UI components. This "learn once, write anywhere" paradigm combines the development efficiency of a cross-platform solution with the high performance and authentic user experience of a native application, making it a cornerstone technology in modern mobile application development.