Difference between Web Server and Application Server?

Most of the times these terms Web Server and Application server are used interchangeably.

Web server: serves content to the web using http protocol.

Web Server is mostly designed to serve static content, though most Web Servers have plugins to support scripting languages like PHP, ASP, JSP etc. through which these servers can generate dynamic HTTP content.

Application server: hosts and exposes business logic and processes. They are well suited for dynamic content.

Most of the application servers have Web Server as integral part of them. Additionally App Server have components and features to support Application level services such as Connection Pooling, Object Pooling, Transaction Support, Messaging services etc.