A disease is endemic when it is always present in a geographical area or a population group.
When the number of cases is greater than what we normally expect, we say there is an outbreak, an epidemic, or a pandemic. An outbreak is limited to a specific area (like a school) within a certain time period; an epidemic occurs when an outbreak spreads to an even larger area (a country, for example), while a pandemic is when an epidemic spreads across borders, even the entire world.