This is a backend framework that is present in Node.js. Any online courses for machine learning and AI provide knowledge to use this framework to write code as Node modules. It helps the coders to design any APIs and other web applications. Express also allows development support through a host of middleware that helps write shorter codes to save time while ensuring quality. Express is mainly used as it is single-threaded, asynchronous, efficient, scalable, and allows reusability of the code. It is a robust API that has the biggest community of online support for Node.js.