The International Association for the Study of Pain defines 'pain' as,

"an unpleasant sensory and emotional experience associated with actual or potential damage or described in terms of such damage".

Although knowledge about pain is based on the experience of humans, there is also a specific definition for 'animal pain' :

"Pain in animals is an aversive sensory and emotional experience, which elicits protective motor actions, results in learned avoidance and may modify species-specific traits of behaviour including social behaviour."

Common to both definitions is the notion that pain is both a sensory and an emotional experience which, at best, is unpleasant and, most often, aversive. This experience serves to minimise or avoid tissue damage and, when damage has been sustained, behaviours can be modified to promote healing and recovery. Behaviours which are directed to achieving these outcomes are important indicators in our diagnosis of pain in animals.