Application server is a server program in a computer and is considered as the middle tier (second part) of the three tier application architecture. The other two parts are the graphical user interface (GUI) and database and transaction server. It is designed to install, operate and anchor applications and other associated services that can be shared among multiple users connecting both local and remote users. It is available as the HTTP server along with the web server in the same computer or in a separate computer. Many large websites house multiple web servers and application servers.
The application server combines with the web server to deliver computer services and applications to other devices. Key functions of application server include minimum downtime, data redundancy, load balancing, data security, user management and a centralized interface. Application servers offer a variety of language systems that include java server pages (JSPs), active server pages (ASPs), and java servlets.