Stress : As it pertains to the term defense physiology, the term stress refers to a perceived threat to the continued functioning of the body / life according to its current state.
A physical event (a loud noise or car collision or a coming attack), a chemical or a biological agent which alters (or has the possibility to alter) body function (physiology) away from optimum or healthy functioning (or away from its current state of functioning) may be perceived as a threat (also called a stressor).
Life circumstances, though posing no immediate physical danger, could be perceived as a threat.
Anything that could change the continuing of the person’s life as they are currently experiencing it could be perceived as a threat.
What is important to the individual, in terms of the body’s response, is that a threat is perceived.