Public health
Public health is "the science and art of preventing disease, prolonging life and promoting health
Health is the level of functional or metabolic efficiency of a living being. In humans, it is the general condition of a person's mind, body and spirit, usually meaning to be free from illness, injury or pain...

 through the organized efforts and informed choices of society, organizations, public and private, communities and individuals" (1920, C.E.A. Winslow
Charles-Edward Amory Winslow
Charles-Edward Amory Winslow was an American bacteriologist and public health expert who was, according to the Encyclopedia of Public Health, "a seminal figure in public health, not only in his own country, the United States, but in the wider Western world."Winslow was born in Boston,...

). It is concerned with threats to health based on population health
Population health
Population health has been defined as “the health outcomes of a group of individuals, including the distribution of such outcomes within the group.” It is an approach to health that aims to improve the health of an entire population. One major step in achieving this aim is to reduce health...

 analysis. The population in question can be as small as a handful of people or as large as all the inhabitants of several continents (for instance, in the case of a pandemic
A pandemic is an epidemic of infectious disease that is spreading through human populations across a large region; for instance multiple continents, or even worldwide. A widespread endemic disease that is stable in terms of how many people are getting sick from it is not a pandemic...