Hi An application server is a generalized server for running more than one applications like EJB, RMI, IIOP, JSP, Servlets, etc. An web server is for the purpose of processing the requests over the Http proptocols.
A Web Server understands and supports only HTTP protocol whereas an Application Server supports HTTP,TCP/IP and many more protocols. Also many more features such as Caches,Clusters,Load Balancing are there in Application Servers which are not available in Web Servers. We can also Configure Application Servers to work as Web Server. In short, Applicaion Server is a super set of which Web Server is a sub set.
Thanks & Regards