Target-organ damage is a research concept and clinical phenomenon referring to structural or functional impairment occurring in specific organs or organ systems that are particularly susceptible to the effects of a disease process, toxic exposure, or chronic physiological stressor. This field investigates the mechanisms, manifestations, progression, and clinical consequences of damage in these 'target' tissues, highlighting their vulnerability and the critical role such damage plays in morbidity, prognosis, and the development of secondary complications associated with underlying conditions or exposures.