A Black Swan Event is a rare and unpredictable occurrence with massive impact. The term comes from the ancient belief that black swans did not exist until they were discovered in nature.

The concept was popularized by statistician Nassim Nicholas Taleb in his 2007 book The Black Swan. He described three key traits of these events:

1. They are outliers, impossible to predict with past data.

2. They have extreme consequences on society, markets, or politics.

3. After they occur, people try to rationalize them as if they were predictable.

Famous Black Swan examples include the fall of the Soviet Union, the 9/11 attacks, and the rise of the internet. In finance, such events often trigger unexpected crashes or disruptions across global markets.