The 1918–20 "Spanish flu" influenza pandemic resulted in dramatic mortality worldwide.

Pandemic

The 1918–20 "Spanish flu" influenza pandemic resulted in dramatic mortality worldwide.
The 1918–20 “Spanish flu” influenza pandemic resulted in dramatic mortality worldwide.

A pandemic is an epidemic of disease that has spread across a large region, for instance multiple continents, or worldwide. A widespread endemic disease with a stable number of infected people is not a pandemic. Widespread endemic diseases with a stable number of infected people such as recurrences of seasonal flu are generally excluded as they occur simultaneously in large regions of the globe rather than being spread worldwide.