A pandemic is an outbreak of disease that is widespread, affecting a large region or even multiple continents. It is characterized by the spread of the disease across a large population, with high rates of infection and transmission from person to person. Unlike an epidemic, which is typically limited to a specific region or community, a pandemic has the potential to affect millions of people around the world. Pandemics are often caused by the emergence of new strains of infectious diseases or the spread of existing diseases to new populations.