Health is a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity. The bibliographic citation for this definition is: Preamble to the Constitution of the World Health Organization as adopted by the International Health Conference, New York, 19 June – 22 July 1946; signed on 22 July 1946 by the representatives of 61 States (Official Records of the World Health Organization, no. 2, p. 100) and entered into force on 7 April 1948. The definition has not been amended since 1948.
Source and further information: http://www.who.int/suggestions/faq/en/