What is "killer application"

n. a technological product that is so good, or so innovatory, that it is irresistible to potential customers; especially a software product that persuades people to buy the hardware needed to use it

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, a programming language, software platform, or an operating system. In other words, consumers would buy the (usually expensive) hardware just to run that application. A killer app can substantially increase sales of the platform on which it runs.