Longman Dictionary of Contemporary English
Wiktionary
n. (context computing English) A set of computer programs which work together to solve a particular problem or to be used for a particular user-defined application.
Wikipedia
An application program (app or application for short) is a computer program designed to perform a group of coordinated functions, tasks, or activities for the benefit of the user. Examples of an application include a word processor, a spreadsheet, an accounting application, a web browser, a media player, an aeronautical flight simulator, a console game or a photo editor. The collective noun application software refers to all applications collectively. This contrasts with system software, which is mainly involved with running the computer.
Applications may be bundled with the computer and its system software or published separately, and may be coded as proprietary, open-source or university projects. Apps built for mobile platforms are called mobile apps.
Usage examples of "application software".
And as I've said, Microsoft's application software tends to be very good stuff.
But now I'm talking about application software, not operating systems.