Public Health: This refers to the science and art of preventing disease, prolonging life, and promoting human health through organized efforts and informed choices of society, organizations, communities, and individuals.
Epidemiology: This is the study and analysis of the distribution (who, when, and where), patterns and determinants of health and disease conditions in defined populations.
Pandemic: A pandemic is an epidemic occurring on a scale that crosses international boundaries, usually affecting a large number of people.