Application server (application server for short). By our definition, as an application server, it exposes business logic to expose client applications over various protocols, including HTTP. Web servers primarily handle sending HTML to browsers for browsing, while application servers provide access to business logic for use by client applications. The application uses this business logic just as if you were calling a method (or a function in a procedural language) on an object.
An application server’s client (including a graphical user interface (GUI)) may run on a PC, a Web server, or even another application server. Information traveling back and forth between an application server and its client is not limited to simple display tags. Instead, this information is program logic. Because this logic takes the form of data and method calls rather than static HTML, clients can use the exposed business logic however they want.
In most cases, application servers expose business logic to client applications through the component application Programming interfaces (apis), An example is the Enterprise Javabeans (EJB) component model based on J2EE(Java 2 Platform, Enterprise Edition) application server. In addition, an application server can manage its own resources, such as gate-keeping duties, including security, transaction processing, resource pooling, And messaging. Like Web servers, application servers employ a variety of scalability and fault tolerance techniques.
Microsoft’s definition of it
We define an application server as “the underlying system software that performs shared business applications as a server.” Just as file servers serve files to many users, application servers make applications (typically client-created applications) available to multiple users simultaneously