Differences between Outbreak, Epidemic, Pandemic and Endemic...

An epidemic is a disease that affects many people at the same time, such as the flu.
The US Centers for Disease Control and Prevention's official definition of epidemic is: 'The occurrence of more cases of disease than expected in a given area or among a specific group of people over a particular period of time'.
A pandemic is a very extensive epidemic, like a plague, that is prevalent in a country, continent, or the world.
There is also the word endemic, which is a disease native to a people or region, which is regularly or constantly found among a people or specific region.
The term outbreak describes the sudden rise in the incidence of a disease, especially a harmful one. An outbreak is characterized by a disease's bypassing of measures to control it.
Often, the difference between these terms is determined by the percentage of deaths caused by the disease.