The 1987 worldwide stock-market crash whose biggest one-day loss came on October 19 was Black Monday.
On October 19, 1987, major equity markets fell sharply around the world. The Dow Jones Industrial Average dropped 22.6 percent, its largest one-day percentage decline in history. The fall followed earlier weakness in markets in Asia and Europe and was amplified by rapid computerized trading and portfolio-insurance strategies.
The episode exposed weaknesses in market infrastructure and raised concerns about whether automatic selling could intensify a panic. Regulators subsequently developed coordinated trading halts, commonly known as circuit breakers, to give markets time to absorb extraordinary order imbalances.
Black Monday is not the same as the 1929 Black Monday or the 2008 crisis. The 1987 crash also did not produce an economic depression on the scale of the 1930s, although it caused substantial losses and lasting changes in market regulation.