In marketing terminology, a killer application (commonly shortened to killer app) is any computer program that is so necessary or desirable that it proves the core value of some larger technology, such as computer hardware, gaming console, software, or an operating system. One of the first examples of a killer application is generally agreed to be the ‘VisiCalc’ spreadsheet for the Apple II. The machine was purchased in the thousands by finance workers on the strength of this program.
The definition of ‘killer app’ came up during Bill Gates’s questioning in the ‘United States v. Microsoft’ antitrust suit. Gates had written an email in which he described ‘Internet Explorer’ as a killer app. In the questioning, he said that the term meant ‘a very popular application,’ and did not connote an application that would fuel sales of a larger product or one that would supplant its competition.
The Daily Omnivore 