Servlets are Java programs that use the Java Servlet Application Programming Interface (API). You must package servlets in a Web ARchive (WAR) file or Web module for deployment to the appserver. Servlets run on a Java-enabled Web server and extend the capabilities of a Web server, similar to the way applets run on a browser and extend the capabilities of a browser.
Servlets can support dynamic Web page content, provide database access, serve multiple clients at one time, and filter data.
For the purposes of IBM WAS, discussions of servlets focus on HTTP servlets, which serve Web-based clients.
See AlsoDeveloping servlets with WAS extensions
Webapplications: Resources for learning