The Value Proposition Canvas is a tool for the collaborative development of the fit beween a customer segment, especially its key jobs and related gains and pains, with potential value propositions which could be provided for the segment. Here is a nice 3′ explanation by the company that designed the canvas, Strategyzer.
Btw, the design may well have been motivated by Strategyzer’s wish to help many users of its popular Business Model Canvas develop, for their products, its key components, namely Customer Segment and Value Proposition.