An outbreak is when many people get sick at the same time due to an illness or disease. It can also mean a sudden and violent event.
Outbreaks are often what happen when there's a flu epidemic, but they can be caused by other things like food poisoning or even animal diseases. When it comes to events, an outbreak is similar to a riot - it's a sudden explosion of strong emotions or actions that gets out of control quickly.
An eruption; the sudden appearance of a rash, disease, etc.
Example: Any epidemic outbreak causes understandable panic.
