The document defines key terms related to stress such as stress, stressors, distress, and eustress. It explains Selye's definition of stress as a nonspecifically induced state manifested by specific physiological changes. The document also describes the general adaptation syndrome (GAS) as having three stages: the alarm stage of initial reaction to stressors, the resistance stage of building tolerance, and the exhaustion stage of vulnerability to stressors due to overtaxed systems.