The International Statistical Classification of Diseases and Related Health Problems, usually called by the short-form name International Classification of Diseases (ICD), is the international "standard diagnostic tool for epidemiology, health management and clinical purposes". The ICD is maintained by the World Health Organization (WHO), the directing and coordinating authority for health within the United Nations System. The ICD is designed as a health care classification system, providing a system of diagnostic codes for classifying diseases, including nuanced classifications of a wide variety of signs, symptoms, abnormal findings, complaints, social circumstances, and external causes of injury or disease. This system is designed to map health conditions to corresponding generic categories together with specific variations, assigning for these a designated code, up to six characters long. Thus, major categories are designed to include a set of similar diseases.