As a general concept, Jobs-to-be-Done is best defined as a perspective — a lens through which you can see and think about markets, customers, needs, competitors, and customer segments in a way that makes innovation far more predictable and profitable.
The notion that people buy products and services to get a job done and that new products and services win in the marketplace if they help customers get a job done better and/or more cheaply. It is synonymous with Jobs Theory.