React Native is an open-source framework developed by Facebook (now Meta Platforms, Inc.) that allows developers to build mobile applications for iOS, Android, and other platforms using JavaScript and React. It is an extension of the React library, which is primarily used for building web user interfaces, adapted for mobile app development.

Key features and concepts of React Native include:

1. Cross-Platform Development: One of the main advantages of React Native is that you can write a single codebase in JavaScript and use it to create native applications for multiple platforms, including iOS and Android. This can significantly reduce development time and maintenance effort compared to building separate native apps for each platform.

2. Native Performance: React Native bridges JavaScript code with native components, allowing developers to build UIs using native components and APIs. This provides near-native performance because the majority of the app's code runs directly on the device's GPU (Graphics Processing Unit) rather than in a web view, as is the case with some other cross-platform frameworks.

3. Reusable Components: React Native encourages the use of reusable UI components. Developers can create components that are shared between different parts of the app or even between different React Native projects. This promotes code reusability and maintainability.

4. Hot Reloading: React Native supports hot reloading, which means that developers can see the results of their code changes almost instantly without the need to recompile the entire app. This can greatly speed up the development and debugging process.

5. Access to Native Modules: While most of the code is written in JavaScript, React Native allows developers to access and use native modules written in languages like Objective-C (for iOS) or Java (for Android) when necessary. This enables developers to leverage platform-specific features or libraries.

6. Large Community and Ecosystem: React Native has a large and active community, which has led to the creation of a vast ecosystem of third-party libraries and plugins that extend its functionality. This ecosystem includes tools for navigation, state management, and more.

7. React DevTools: Developers familiar with React for web development can use React DevTools to inspect and debug React Native applications.

8. Integration with Existing Native Code: React Native can be integrated into existing native projects, allowing developers to gradually adopt it and reuse existing code.

React Native is a popular choice for mobile app development, especially for projects that require rapid development, code sharing between platforms, or when a development team has expertise in JavaScript and React. It has been used by many companies to build high-profile mobile apps, including Facebook, Instagram, Airbnb, Uber, and many others.

Keep in mind that while React Native can be a powerful and efficient way to build cross-platform mobile apps, it may not be the best choice for every project. Factors such as project requirements, performance goals, and the need for platform-specific features should be considered when choosing a mobile development framework.