Black Monday was the name of the first trading day of extreme global selling in the 1987 stock-market crash.
Black Monday refers to October 19, 1987, when stock markets around the world fell sharply. In the United States, the Dow Jones Industrial Average lost 22.6 percent, its largest one-day percentage decline. Hong Kong and European markets had already suffered major falls, and the selling continued across time zones.
The phrase is not unique to 1987. “Black Monday” has also been used for other severe market declines, including October 28, 1929, in the United States. That overlap can create confusion when a question does not specify the year. In financial history, the 1987 reference is usually identified by the date or by the record-setting Dow decline.
The event led to reforms in trading systems, including circuit breakers that temporarily halt markets after large moves. These measures aim to slow panic and give participants time to evaluate rapidly changing prices.