Stress is an altered physiological condition caused by factors that tend to disrup tthe equilibrium. Strain is any physical and chemical change produced by a stress (Gasparetal., 2002). The term stress is used with various meanings, the physiological definition and appropriate term as responses in different situations.

Stress is simply a fact of nature forces from the outside world affecting the individual. The individual responds to stress in ways that affect the individual as well as their environment. Hence, all living creatures are in a constant interchange with their surroundings (the ecosystem), both physically and behaviorally.

The events that provoke stress are called stressors, and they cover a whole range of situations everything from outright physical danger to making a class presentation or taking a semester's worth of your toughest subject.