An Etymological Dictionary of Astronomy and Astrophysics

1. General: The act of applying to a particular purpose or use.
   

2. Computers: A program that performs a specific function for the user, as contrasted with an environment or operating system. Some examples are Microsoft Windows, Microsoft Word, and Adobe Photoshop. The word “application” is used because each program has a specific application for the user.
   

See also: Verbal noun of → apply.