Web server and Application server

A Web server can execute only Web applications.The Web applications are usually stored on a server and delivered to users over the Internet. The Web server takes the HTTP request, then passes it to a server-side program (Servlets, JSPs, ASPs, CGI Scripts...) to handle the request. Once processed, the HTML response is sent back to your Web browser.

In short web server simply serves pages for viewing in web browser. Examples: Apache Web server, Google Web server

An application server is capable of executing Enterprise applications.It can act as a simple Web server or can run Enterprise business logic.For example, a J2EE application server exposes the business logic through a component API (Such as an Enterprise JavaBean component).Then a client application program (Say a GUI running on a PC, a Web server, or even other application server) can employ this exposed business logic however it wants.

It implies an application server can support HTTP,TCP/IP and many more protocols.In addition, application server also has extra features like security, transaction processing, resource pooling and messaging. Examples: Websphere, Jboss, Weblogic