The term stress was coined by Hans Selye in 1976, where he defined it as a “nonspecific response by the body to any demand made upon it”. Selye proposed a theory of stress, which he called the general adaptation syndrome, stating that the organism undergoes a predictable three-stage process when reacting to stressors. The three stages are the alarm phase (acute mobilization of energy), resistance phase (a more prolonged and less intense mobilization of energy), and the exhaustion phase (the body is drained of its energy resources, and is no longer able to maintain a response).

Source:

Selye H. (1976). Stress in health and disease. Reading, MA: Butterworth.