An application server is a product that is essentially component based and one that is present in the middle tier level of a server based architecture. It provides services for security as well as maintenance coupled with data access as well as persistence. Simply put, an application server is nothing but a software framework that succeeds in providing facilities for creating web applications as well a suitable server based environment for running them. Most frameworks for application servers contain a comprehensive layer model for service.
So what then is an application? In terms of information technology, an application is nothing but a computer program that is designed for helping people to perform an activity. Therefore, an application differed from an operating system which runs on a computer as well as a utility function which is responsible for performing general chores and tasks or even a programming tool with the help of which computers are created.
Primarily, the term application server was used for discussing client server systems in early days for differentiating servers which contain SQL services as well as for isolating middle-ware services from other kinds of servers. It is often mistaken to be considered as a web application environment.