What is the term for when a disease spreads rapidly affecting many people?

The term that describes a disease spreading rapidly and affecting a large number of people is "epidemic." An epidemic occurs when the incidence of a disease exceeds what is normally expected in a specific area or population. It highlights a sudden increase in cases of a disease that can create significant health care challenges and public concern.

While "outbreak" generally refers to a similar increase, it often implies a smaller scale or a specific location. "Pandemic" describes a global spread of a disease that affects multiple countries or continents, usually involving a higher level of severity. "Prevalence" refers to the total number of cases of a disease in a population at a given time but does not specifically denote a rapid spread.

Thus, the correct term for a disease that spreads rapidly affecting many people is "epidemic."