Pain, in the sense of physical pain, is a typical sensory experience that may be described as the unpleasant awareness of a noxious stimulus or bodily harm. Individuals experience pain by various daily hurts and aches, and occasionally through more serious injuries or illnesses. For scientific and clinical purposes, pain is defined by the International Association for the Study of Pain (IASP) as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage".
Pain is highly subjective to the individual experiencing it. A definition that is widely used in nursing was first given as early as 1968 by Margo McCaffery: "'Pain is whatever the experiencing person says it is, existing whenever he says it does".