[1] It directs a deployment tool to deploy a module or application with specific container options, security settings and describes specific configuration requirements.
XML is used for the syntax of these deployment descriptor files.
For Java EE applications, the deployment descriptor must be named application.xml and must be placed directly in the META-INF directory at the top level of the application .ear file.
[1] The Java EE deployment descriptors are defined by the language specification,[2] whereas the runtime descriptors are defined by the vendor of each container implementation.
For example, the web.xml file is a standard Java EE deployment descriptor, specified in the Java Servlet specification, but the sun-web.xml file contains configuration data specific to the Sun GlassFish Enterprise Server implementation.