The International Association for the Study of Pain (IASP) defines it as: An unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of such damage. The IASP definition means that pain is a subjective experience; one that cannot be objectively measured and depends on the person’s self-report. As will be discussed later, there can be a wide variability in how a person experiences pain to a given stimulus or injury.