A Definition for Stress
The English language is quite complex and enigmatic because it allows us to take an idea or concept and apply it to seemingly unrelated areas, instead of making a whole new word. To some, this displays adaptability and versatility; to others it blurs the word's definition, making it more ambiguous.
"Stress" is an excellent example. When speaking, one can change the vocal intonation of a syllable or word which emphasizes something the speaker feels is important. So we could say that the speaker has put stress on a part of the sentence. In terms of physical things like tools, bones, and furniture; the point where they break is said to be the point of the most stress, as stress describes the force that deforms an object.
The brain essentially has 2 underlying primal mental states: Fight-or-Flight, and Rest-and-Digest. Essentially, when the body experiences the former then the bowels stop digesting food, vision and thought processes change, there's a flood of hormones dumped into the blood that increase the heart beat, blood pressure, reduce the sensation of pain and fight fatigue. These changes are necessary for the body to have the ability to sprint to safety, or defend itself from attack. The latter is the exact opposite, which allows the body to meditate, heal from injury, fight infections, digest food, and sleep.
Because we still have these primal instincts but live in a highly sophisticated society, there are factors that push us from Rest-and-Digest and into Fight-or-Flight, even though we aren't in danger. We've used the word "Stress" to refer to these factors since the 1920's. Some stressors, like social interaction, will never go away no matter how our society changes. However others, like traffic jams, are a product of our own making.
It's important to take the time to identify the stressors that we have. Once we're aware of where our stress comes from, we can take steps to change it.
Dan