killer app
The application that actually makes a sustaining market for a
promising but under-utilized technology. First used in the
mid-1980s to describe Lotus 1-2-3 once it became evident that
demand for that product had been the major driver of the early
business market for IBM PCs. The term was then restrospectively
applied to VisiCalc, which had played a similar role in the
success of the Apple II. After 1994 it became commonplace to
describe the World Wide Web as the Internet's killer app. One of
the standard questions asked about each new personal-computer
technology as it emerges has become "what's the killer app?"