A pandemic is defined as the global or large-scale spread of an infectious disease that results in a sudden, significant increase in the number of cases. Unlike localized epidemics, a pandemic affects a substantial portion of the human population across multiple continents or the entire world. The term emphasizes the geographic reach and the rapid expansion of the disease.
It is important to distinguish pandemics from endemic diseases, which maintain a relatively stable number of infections within a population over time. For example, seasonal influenza is typically not classified as a pandemic because its occurrence is predictable and does not represent a sudden, worldwide surge in new cases. Pandemics represent extraordinary events that often require coordinated international responses to manage their impact.