ReactiveX is a programming paradigm that combines the principles of reactive programming with the observer pattern. It allows developers to work with asynchronous data streams, making it easier to handle events and changes over time. By using observables, observers, and operators, ReactiveX enables the creation of flexible and responsive applications. The core idea of ReactiveX is to treat data as a stream that can be observed and manipulated. This approach simplifies the management of complex data flows, especially in applications that require real-time updates, such as web applications and mobile apps. ReactiveX is implemented in various programming languages, including JavaScript, Java, and Python.