A pandemic ( ) is an epidemic of an infectious disease that has spread across a large region, for instance multiple continents or worldwide, affecting a substantial number of individuals. A widespread endemic disease with a stable number of infected individuals is not a pandemic. Widespread endemic diseases with a stable number of infected individuals such as recurrences of seasonal influenza are generally excluded as they occur simultaneously in large regions of the globe rather than being spread worldwide. Throughout human history, there have been a number of pandemics of diseases such as smallpox. The most fatal pandemic in recorded history was the Black Death—also known as The Plague—which killed an estimated 75–200 million people in the 14th century. The term had not been used then but was used for later epidemics, including the 1918 influenza pandemic—more commonly known as the Spanish flu. Current pandemics include HIV/AIDS and COVID-19. Definition A pandemic is an epidemic occurring on a scale that crosses international boundaries, usually affecting people on a worldwide scale. A disease or condition is not a pandemic merely because it is widespread or kills many people; it must also be infectious. For instance, cancer is responsible for many deaths but is not considered a pandemic because the disease is not contagious—i.e. easily transmittable—and not even simply infectious. In 2009, the World Health Organization (WHO) dropped the words "with enormous numbers of deaths and illness" from their definition. In 2008, it also dropped the requirement of an "influenza pandemic" to be a new sub-type with a simple reassortant virus, meaning that many seasonal flu viruses now could be classified as pandemic influenza. The word comes from the Greek παν- pan- meaning "all", or "every" and δῆμος demos "people". Assessment Stages The World Health Organization previously applied a six-stage classification to describe the process by which a novel influenza virus moves from the first few infections in humans through to a pandemic. It starts when mostly animals are infected with a virus and a few cases where animals infect people, then moves to the stage where the virus begins to be transmitted directly between people and ends with the stage when infections in humans from the virus have spread worldwide. In February 2020, a WHO spokesperson clarified that "there is no official category [for a pandemic]". During the 2009 influenza pandemic, Dr. Keiji Fukuda, Assistant Director-General ad interim for Health Security