The TOC Dictionary provides the following definition:
Decisive Competitive Edge (DCE)
A significant sustainable market advantage over competitors.
Usage: A DCE exists only if an organization satisfies a significant market need to an extent that no significant competitor can. In many situations, competitors are unaware of the problems their industry or the conventional mode of operation creates for their customers. An examination of the problems the industry creates for its customer is the starting point for identifying a potential DCE. Price is never considered a DCE. Availability, inventory turns, or reliability are potential retailer‘s significant needs and can be turned into a DCE.
A DCE is similar to the traditional concept of competitive advantage but differs in the mechanisms used to identify the DCE. The DCE is identified through an analysis of customer problems created by the suppliers‘ industry.
Cox III, James F., Lynn H. Boyd, Timothy T. Sullivan, Richard A. Reid, and Brad Cartier, 2012, The Theory of Constraints International Certification Organization Dictionary, Second Edition, page 42.