An epidemic is a rapid spread of infectious disease affecting many people within a specific geographic area or population at the same time. Epidemics occur when disease incidence significantly exceeds normal expectations for a community. The term differs from endemic (disease constantly present at expected levels), outbreak (small localized increase), and pandemic (global epidemic affecting multiple countries). Public health authorities monitor disease patterns to detect epidemics early, enabling rapid response through testing, contact tracing, quarantine, treatment, and public communication. Historical epidemics have significantly shaped public health systems and infrastructure. While COVID-19 was a pandemic (global spread), communities experienced local epidemics with varying intensity. Municipal public health units play crucial roles in epidemic response, working with provincial health ministries and the federal Public Health Agency of Canada.