"Black Monday" refers to October 19, 1987, when stock markets around the world crashed dramatically. The Dow Jones Industrial Average fell by over 22% in a single day, marking one of the largest one-day percentage declines in history. This sudden drop was attributed to a combination of factors, including high inflation, rising interest rates, and panic selling. The crash had widespread effects, leading to significant losses for investors and prompting concerns about the stability of the global economy. In response, regulatory bodies implemented new measures to prevent future market crashes, including the introduction of circuit breakers to temporarily halt trading during extreme volatility.