The World Health Organization defines health as a positive concept, stating that it is "a state of complete physical, psychological and social well-being and not merely the absence of disease or infirmity." This seems rather ambitious, particularly in the inclusion of a social element, and may also lead us on to the further inquiry: "What is well-being?" Many dictionaries, including the Oxford English Dictionary, list precisely the the meaning which the WHO rejects, "freedom from illness or injury," as the primary meaning of health. Since we talk about good health and bad health, however, it may be helpful to regard health as a spectrum rather than an absolute. Someone who conforms to the WHO definition is in excellent health, but one may also be in good, fair, neutral, or poor health among the different measures it lays out.
It is fair to say that the same is applicable to illness, with the caveat that health is general, whereas illness is specific. It is admittedly less specific than the concept of "disease," which relates directly to the measurable, biological dimension of illness, but we would still expect a person complaining of illness to be able to describe approximately what sensation the individual feels and what part of the body it affects. Doctors rely on such descriptions as an important part of diagnosis, which remains an art as well as a science. Illness, therefore, is generally localized and a specific illness may affect part of the body of a subject who otherwise enjoys good health.