A black swan is an event or occurrence that is deemed unpredictable, and therefore impossible to predict. The term was popularized by Nassim Taleb in his book of the same name, which discusses the unpredictability of rare events in finance and other fields. Black swans can be positive or negative events; for example, a company's successful IPO may be seen as a positive black swan, while its bankruptcy would be seen as a negative black swan. Black swans are typically outside of the realm ...