Final answer:
An enhancement project involves adding new capabilities or features to an existing system to improve functionality or user experience.
Step-by-step explanation:
The term enhancement project refers to a type of project within software development, systems engineering, or information technology aimed at improving an existing system. An enhancement project typically focuses on adding new capabilities or features to the system to increase its functionality, correct deficiencies, improve user experience, or maintain its relevance in a changing technology landscape. Among the given options, the best definition for an enhancement project is D: Enhancement project is one in which new capabilities are added to an existing system.