What is defined as a widespread outbreak of an infectious disease?

The term that defines a widespread outbreak of an infectious disease is "pandemic." A pandemic refers to an epidemic that has spread over several countries or continents, affecting a large number of people.

To clarify the other terms: "epidemic" refers specifically to a disease that affects a large number of people within a particular community or region during a specific time frame, but it is less broad than a pandemic. An "endemic" is a disease or condition regularly found and consistently present in a particular geographic area, while an "outbreak" generally signifies a sudden increase in the number of cases of a disease beyond what is normally expected, which may be localized or regional.

Understanding these distinctions helps to clarify the scope and scale of disease spread, with "pandemic" representing the most extensive level, indicating global reach and impact.