Express JS development is the process of creating web applications using the Express JS framework, a popular Node.js framework. It involves building scalable, efficient, and robust web applications that can handle large volumes of traffic. Express JS development typically involves creating APIs, middleware, and server-side rendering. It requires proficiency in JavaScript, Node.js, and various tools and libraries. The development process also involves using databases, such as MongoDB and MySQL, and integrating with other third-party services. Finally, testing and debugging are crucial components of the development process to ensure the application is stable and secure.