Stress is only defined by each individual's own ability to cope with the specific situation.
Stress can be either positive or negative.
In fact, without a certain amount of stress none of us could function properly. Positive stress for instance would be the nervousness a performer may experience before going out onto stage. This sort of stress can help us to perform to the best of our ability. However, when stress is allowed to build up to an excessive level it becomes negative stress. Regardless of how stress is initially caused the body appears to respond to it in three stages.