An application system normally consists of a user interface, business logic and a database of some sort. The user interface is something that you can see and something that is used to interact with the computer.  It could consist of set of screens, web pages or reports.  Sometimes the user interface is an input device such as a bar code reader or a voice recognition device.  Some application systems don't have non-visual interfaces.  These application systems exchange data electronically with other applications via a network.