Stress is the body's response to perceived threats or demands. It involves physiological reactions like increased heart rate and hormones like cortisol. Prolonged stress can negatively impact health. Early pioneers like Walter Cannon studied stress and identified the fight or flight response. Later, Hans Selye proposed the general adaptation syndrome model of stress involving alarm, resistance, and exhaustion stages. The transactional model views stress as resulting from an imbalance between demands and one's ability to cope, determined through cognitive appraisals. Acute and chronic stress can have positive or negative impacts depending on factors like duration and perception.