The first trading day of exceptionally severe global losses in the 1987 market crash was called Black Monday. The name most specifically refers to October 19, 1987, when markets around the world plunged.
The U.S. Dow Jones Industrial Average fell 22.6% that day, its largest one-day percentage decline. The fall followed sharp losses in several overseas markets and was amplified by concerns about valuations, interest rates, currency movements, and automated trading strategies.
The label can cause confusion because financial history contains several “Black” market days. Black Thursday and Black Tuesday are associated with the 1929 Wall Street Crash, while Black Monday also refers to major market declines in other years and countries.
After 1987, market authorities reviewed trading mechanisms and adopted safeguards designed to interrupt extreme movements. These measures did not eliminate volatility, but they aimed to give investors and exchanges time to process information during disorderly conditions.