A minimalist and unopinionated framework that’s part of the popular MEAN stack, Express is the de facto server framework for Node.js. That surely has to do with two of its most notable characteristics: how minimal it is and how powerful it can be (through plugins). And if you add to that the fact that Express has a remarkable performance, you can understand why Express is such a top framework.
Express.js, or simply Express, is a back end web application framework for Node.js, released as free and open-source software under the MIT License. It is designed for building web applications and APIs.