In the past four decades, a number of usefuldefinitions of stress have been developed by researchers. We provide arange of these below: 

Stress arises whenindividuals perceive that they cannot adequately cope with the demandsbeing made on them or with threats to their well-being. R.S. Lazarus(1966). Psychological stress and the coping process. New York:McGraw-Hill. 

Stress, it is argued, can onlybe sensibly defined as a perceptual phenomenon arising from acomparison between the demand on the person and his or her ability tocope. An imbalance in this mechanism, when coping is important, givesrise to the experience of stress, and to the stress response. T. Cox(1978). Stress. Basingstoke: Macmillan Education. 

Stress results from an imbalance between demands and resources. R.S.Lazarus and S. Folkman (1984). Stress, Appraisal and Coping. New York:Springer. 

Stress is the psychological,physiological and behavioural response by an individual when theyperceive a lack of equilibrium between the demands placed upon them andtheir ability to meet those demands, which, over a period of time,leads to ill-health. S. Palmer (1989). Occupational stress. The Healthand Safety Practitioner, 7, (8), 16-18. 

A simple definition that can be used is: Stress occurs when pressure exceeds your perceived ability to cope. 

S. Palmer, 1999.