What is Public Health?

Legal Definition
Public health refers to "the science and art of preventing disease, prolonging life and promoting human health through organized efforts and informed choices of society, organizations, public and private, communities and individuals." It is concerned with threats to health based on population 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). The dimensions of health can encompass "a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity", as defined by the United Nations' World Health Organization. Public health incorporates the interdisciplinary approaches of epidemiology, biostatistics and health services. Environmental health, community health, behavioral health, health economics, public policy, insurance medicine, mental health and occupational safety and health are other important subfields.

The focus of public health intervention is to improve health and quality of life through prevention and treatment of disease and other physical and mental health conditions. This is done through surveillance of cases and health indicators, and through promotion of healthy behaviors. Examples of common public health measures include promotion of hand washing, breastfeeding, delivery of vaccinations, suicide prevention and distribution of condoms to control the spread of sexually transmitted diseases.

Modern public health practice requires multidisciplinary teams of public health workers and professionals including physicians specializing in public health/community medicine/infectious disease, psychologists, epidemiologists, biostatisticians, medical assistants or Assistant Medical Officers, public health nurses, midwives, medical microbiologists, environmental health officers / public health inspectors, pharmacists, dentists, dietitians and nutritionists, veterinarians, public health engineers, public health lawyers, sociologists, community development workers, communications experts, bioethicists, and others.

There is a great disparity in access to health care and public health initiatives between developed nations and developing nations. In the developing world, public health infrastructures are still forming.
-- Wikipedia
Legal Definition
As one of the objects of the police power of the state, the "public health" means the prevailingly healthful or sanitary condition of the general body of people or the community in mass, and the absence of any general or widespread disease or cause of mortality.
-- Black's Law Dictionary