An epidemic is

a widespread outbreak of a disease that affects a large number of people in a specific geographic area or population. The disease can spread rapidly and infect a large proportion of the population, causing illness, disability, and even death. Epidemics can be caused by a variety of factors, including viral or bacterial infections, environmental factors, or other medical conditions. They can affect both humans and animals, and can have significant social, economic, and political consequences. Effective public health measures and vaccination programs can be critical in controlling and preventing the spread of epidemics.