Thank you Jeanne, that was very kind of you to respond.
What I know is that the J2EE 1.4 spec instructs that a web container (that handles servlets and jsp) and EJB container (that implements business component) together make an Application Server. Then what is HTTP server? Apache has an HTTP server project. Is that too an application server? Does an ordinary web servers have containers?
Here is how I look at it, HTTP/Webserver is a webserver such as apache that serves static content (.html, .shtml etc..). A web application server is a webserver that possibly provides an application specific language like PHP/ASP to provide scripting support for applications on top of the webserver. Also I would consider Tomcat a web application server because it does not provide the application framework for distribution objects. An application server on the other hand provides J2EE/.NET application modules/ejb that provide the logic for the application. In other words they contian the application logic or business methods of the application hence the name application server. Hope this helps because I just confused myself :-)