A "black swan" is a term used to describe an unexpected event that has a significant impact. These events are often rationalized in hindsight, making them seem predictable, even though they were not anticipated. The concept was popularized by Nassim Nicholas Taleb, a statistician and author, in his book titled "The Black Swan." In nature, black swans are real birds native to Australia. They are known for their striking black feathers and red beaks. Unlike the more common white swans, black swans symbolize rarity and uniqueness, which aligns with the metaphorical use of the term in discussing unpredictable events in various fields, including finance and history.