An application is a software program running on a computer system or mobile device. It is designed to perform a specific function for the user or other applications and called application because it can be applied for a particular purpose or use.
Applications can be text processing and spreadsheet software, email programs, messaging programs, web browsers, games, etc.
An application usually runs on top of the services provided by an operation system, or another system software that runs in the background and enables the application to run.
In Microsoft Windows, applications may also be referred to as executables or programs. In other systems as mobile devices, they often are simply referred to as apps.