RxJava is a reactive programming library for Java, enabling developers to work with asynchronous and event-driven data streams. It introduces the concept of observables, which emit data that can be processed by operators in a declarative manner. RxJava simplifies complex tasks such as handling API calls, user inputs, and real-time updates. It integrates seamlessly with Android, allowing developers to create responsive and dynamic applications. The library is ideal for building applications that require smooth data flows and user interactions.