What Is a Black swan?
A Black swan is an unpredictable event that is beyond what is normally expected of a situation and has potentially severe consequences. Black swan events are characterized by their extreme rarity, severe impact, and the widespread insistence they were obvious in hindsight.

Black swan events can cause catastrophic damage to an economy by negatively impacting markets and investments, but even the use of robust modeling cannot prevent a Black swan event.
https://www.investopedia.com/terms/b/Blackswan