Deployment descriptor is a configuration file named web.xml that specifies all the pieces of a deployment. It allows us to create and manipulate the structure of the web application. Deployment descriptor describes how a web application or enterprise application should be deployed. For web applications, the deployment descriptor must be called web.xml and must reside in a WEB-INF subdirectory at the web application root. Deployment descriptor allows us to modify the structure of the web application without touching the source code.