If a human disease breaks out across a large region of the world, what is it called?

The correct answer is Pandemic. A pandemic is an epidemic that spreads across countries or continents and affects people over a very large part of the world. The key phrase in the question is 'large region of the world', which points to wide geographic spread rather than a local cluster.

• Epidemic: an unusual rise in cases of a disease within a community, region or country, above the expected level. It is limited in geographic scope, so it describes a regional outbreak, not a global one.
• Endemic: a disease that is constantly present at a baseline level in a particular area, such as malaria in parts of tropical Africa. The defining idea is persistence, not spread.
• Epizootic: an outbreak among animals. The question asks about a human disease, so this is ruled out.

Core concept: diseases are classified by their spread (endemic, epidemic, pandemic). The WHO declared COVID-19 a pandemic in March 2020, a standard recent example. For Mains, these terms recur in health governance and disaster management questions under GS-II and GS-III.

Trap: candidates pick Epidemic because it sounds bigger. Epidemic means excess cases in a defined area; pandemic needs multi-country or global spread.