Final answer:
A worldwide epidemic is called a pandemic, which is an infectious disease that spreads across multiple populations or continents, or even worldwide. Influenza and HIV/AIDS are examples of pandemics when they spread on a global scale.
Step-by-step explanation:
A worldwide epidemic is called a pandemic. Such diseases are not just confined to a single population or region but spread across multiple populations or continents, and sometimes even worldwide. Examples of pandemic diseases include HIV/AIDS and influenza when they spread globally.
An endemic disease, in contrast, maintains a relatively constant presence in a particular area or population. An epidemic refers to a disease outbreak that affects a large number of individuals within a population at the same time, but it's confined to one region or population. Influenza, as an example, is a disease that typically spreads in seasonal epidemics, but when a new and virulent strain emerges, it can lead to a pandemic. The influenza pandemic of 1918, also known as the Spanish Flu, is one of the most devastating examples of a pandemic in modern history, with tens of millions of fatalities.