The World Health Organization's 1948 constitution defines health as 'a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity,' a definition that deliberately moves beyond the absence of illness. Public health focuses on populations rather than individual patients, using prevention, policy, and education to improve health at scale, which is distinct from clinical medicine's focus on diagnosing and treating one patient at a time. The WHO's 2008 Commission on Social Determinants of Health, chaired by Sir Michael Marmot, concluded that factors like income, education, housing, and employment shape health outcomes as much as, or more than, access to healthcare itself -- a finding often summarized as 'the social determinants of health.' This is why public health interventions often target things that look unrelated to medicine at first glance, such as clean water access, road safety, or school attendance, because these factors measurably reduce disease and death at a population level.