Pain Clinic:

Pain is a distressing feeling often caused by intense or damaging stimuli. The International Association for the Study of Pain's widely used definition defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage"; however, due to it being a complex, subjective phenomenon, defining pain has been a challenge. In medical diagnosis, pain is regarded as a symptom of an underlying condition.