Hi
There are lotes of different kinds of server (anything that responds to a client). But what I think you want to know is this:
Web server - think Apache servers up web content (HTML, etc) and can be extended with plugins (CGI, PHP, etc.)Servlet Container - e.g. Tomcat, hosts servlets/jsps and used to serve dynamic content (usually to http clients)EJB container - Used to host EJBs and can serve many clients.Application server - Weblogic, Websphere, Glassfish, JBoss, etc. Typically consists of a web server, servlet container and EJB container. Often provides other stuff as well. Depending on your needs, you would use some or all of the servers available. If you only have static content, then a web server will do. You can often implement all of an application using JSP/Servlets (and maybe a web server upfront). Occasionally, you will have a large scale, transactional system and you could use an EJB container (probably with the other servers as well).
Hope this clears things up
Ramen