Final answer:
Hans Selye, an endocrinologist and stress researcher, defined stress as a relationship between demands and the power to deal with them without unreasonable or destructive costs.
Step-by-step explanation:
The definition of stress as "a relationship between demands and the power to deal with them without unreasonable or destructive costs" was proposed by Hans Selye, an endocrinologist and a prominent stress researcher. Selye's definition of stress focuses on the physiological responses of the body to various demands or situations.