In a very broad spectrum, if we decide to give a definition of stress, we can say
WHAT STRESS IS OUR STYLE
Stress is the body's response to changes in the environment, which is affecting our lives. In each individuals life, there is constant bevy of changes happening. Adjusting and adapting to these changes is inevitable. But this effort of adapting to changes definitely leaves us with a legacy of stress to deal with.
We can broadly define the reasons, as to why stress overtakes our lives, but we need to also understand, that stress us a normal part of everyday life for most people. We need to also understand it's causes and challenges, and then look for our personal way of dealing with it.