Eustress means beneficial stress—either psychological, physical (e.g. exercise), or biochemical/radiological (hormesis). The term was coined by endocrinologist Hans Selye, consisting of the Greek prefix eu- meaning "good", and stress, literally meaning "good stress". It is the positive cognitive response to stress that is healthy, or gives one a feeling of fulfillment or other positive feelings. Selye created the term as a subgroup of stress to differentiate the wide variety of stressors and manifestations of stress.