Which term describes a disease that affects the majority of the population of a large region?

The term that describes a disease affecting the majority of the population of a large region is "pandemic." A pandemic refers to an outbreak of a disease that spreads over multiple countries or continents, affecting a significant number of individuals. It indicates a widespread prevalence that goes beyond local or regional outbreaks.

For instance, the COVID-19 outbreak was declared a pandemic because it affected a large proportion of the world's population, crossing national and continental boundaries. This term highlights the extensive reach and impact of the disease at a global scale, contrasting with other terms which have more specific implications regarding geographical spread and population impact.

Epidemic, on the other hand, typically describes a sudden increase in the number of cases of a disease within a specific area or population. Endemic refers to diseases that are consistently present within a particular geographic area or population. Infectious simply refers to diseases caused by pathogens, such as bacteria or viruses, and does not imply any information about the scale of their spread.