A<unk>  (from Greek , , "all" and , , "local people" the 'crowd') is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic disease with a stable number of infected individuals is not a<unk> . Widespread endemic diseases with a stable number of infected individuals such as recurrences of seasonal influenza are generally excluded as they occur simultaneously in large regions of the globe rather than being spread worldwide. Throughout human history, there have been a number of<unk> s of diseases such as smallpox. The most fatal<unk>  in recorded history was the Black Death—also known as The Plague—which killed an estimated 75–200 million people in the 14th century. The term was not used yet but was for later<unk> s including the 1918 influenza<unk> —the Spanish flu. Recent<unk> s include tuberculosis, Russian flu, Spanish flu, Asian flu, cholera, Hong Kong flu, HIV/AIDS, and COVID-19.
Pandemic
Epizootic
Epidemic
Breakthrough infection
Acute 
Preclinical development
Postdrome
Flu season