Relating to a disease or pathogen that is found in or confined to a particular location, region, or people. Malaria, for example, is endemic to tropical regions.
1662, from Gk. endemos “native,” from en- “in” + demos “people, district”.
An outbreak of a disease or illness that spreads rapidly among individuals in an area or population at the same time.
1603, from Gk. epidemia “prevalence of an epidemic disease”, from epi- “among, upon” + demos “people, district”.
An epidemic that spreads over a very wide area, such as an entire country or continent.
1666, from Gk. pandemos “pertaining to all people,” from pan- “all” + demos “people, district”.
Endemic, epidemic and pandemic are three words that refer to the spread of infectious diseases among a population, but on different scales, as their etymology suggests. An infection is endemic when it affects a very specific and limited group of people and is constant and at a stable rate, an epidemic occurs when new cases of a certain disease in a given human population, during a given period, substantially exceed the normal rate, and a pandemic indicates a far higher number of people and a much larger region affected than an epidemic.
In the case of swine flu, it thus seems appropriate to use the term “pandemic”: the number of people with the disease is still small, but the rate of infection is above normal and the disease is present on several continents.

Piglet photo by crispyking