What is a pandemic?
A pandemic is a disease that has spread to more than a local region possibly even world wide such as the Spanish flu of 1918-1919. Not all pandemics are emergency situations, AIDS is considered a pandemic but not one that you need to prepare for unless it would mutate and become airborne.
Dangers of a Pandemic
The danger would depend on the type of disease and the severity but generally besides contracting the disease it self the main danger would be civil unrest.