Almost all of us have experienced pain; we learn the application of the word through early life experiences with (hopefully minor) injury. What one person finds painful might be a minor discomfort for another, and the line between what we call uncomfortable and what we call painful can shift depending on context and mood.
When we’re talking with others, though, common definitions are vital. Doctors and scientists who work with pain, of course, require very distinct definitions. The International Association for the Study of Pain defines pain as, “An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage.” They go on to qualify it further:
The inability to communicate verbally does not negate the possibility that an individual is experiencing pain and is in need of appropriate pain-relieving treatment. Pain is always subjective. Each individual learns the application of the word through experiences related to injury in early life. Biologists recognize that those stimuli which cause pain are liable to damage tissue. Accordingly, pain is that experience we associate with actual or potential tissue damage. It is unquestionably a sensation in a part or parts of the body, but it is also always unpleasant and therefore also an emotional experience. Experiences which resemble pain but are not unpleasant, e.g., pricking, should not be called pain. Unpleasant abnormal experiences (dysesthesias) may also be pain but are not necessarily so because, subjectively, they may not have the usual sensory qualities of pain. Many people report pain in the absence of tissue damage or any likely pathophysiological cause; usually this happens for psychological reasons. There is usually no way to distinguish their experience from that due to tissue damage if we take the subjective report. If they regard their experience as pain, and if they report it in the same ways as pain caused by tissue damage, it should be accepted as pain. This definition avoids tying pain to the stimulus. Activity induced in the nociceptor and nociceptive pathways by a noxious stimulus is not pain, which is always a psychological state, even though we may well appreciate that pain most often has a proximate physical cause.
(“ IASP Terminology – IASP ,” 2017)
Yes, this does imply that masochists engaging in “pain play” are experiencing something that cannot be considered pain in the clinical sense. (Wegemer, 2018)