Express is a lightweight and flexible Node.js framework that offers a wide range of features for mobile and web applications. It is easy to create a robust API using a variety of HTTP utility methods and middleware. Express offers a thin layer that covers the core web application features without obscuring the Node.js features you already love. Express does not have any notion of a database. Third-party Node modules allow you to interface with almost any database. Express does not recognize 404 responses as errors and will not capture them. This is because a response of 404 indicates that there is no additional work to be done. Express has executed all middleware functions, routes, and found none of them to be responsive.