The software that an End User directly interacts with to accomplish some operationally relevant task (“business logic”). Application software is usually specific to an OS, or OS family, but can be written so as to be portable. Application software is sometimes referred to as a “program”, “application program” or, more recently, an “app”.
See also device driver, tool, utility, and middle-ware which are here considered to be special cases of Application Software, requiring special distinction in the perspective of programmers and Software System Engineers.