Stress = tension.

It is the experienced tension when you effectivly need to respond in a situation.

Complaints of stress emerge when the tension and relaxation are no more in balance. Or when you think that your possibbilities to respond are out numbered by the demands of your (working) environment.

One of the easiest ways to understand the solution, is to view the stress model created by Albert Ellis. He calls is the ABC-model:

The A of activating factor: the thing that activates your stress, the potential stress creating situation or event.

The B of beliefs or your view: your experiences, thoughts, interpretations or beliefs concerning the situation.

The C of consequences: the emotional consequences or the stress coming from your experiences, thoughts, interpretations or beliefs concerning the situation.

In other words:

A potentially stress causing situation A -> your way of dealing with it B -> Experiencing stress C .