The run time for dynamic Web applications. WAS includes support for Java servlets, Java ServerPages (JSPs), and other enterprise Java application programming interfaces (APIs). WAS provides communications, resource management, security, transaction management, and persistence capabilities for Web applications. It also typically includes an administration interface for managing the server and deployed applications.

An application server that is linked to a Web server. When the Web server receives an HTTP request that requires computation or other resources, it passes the request to the Web application server for processing.