October 19, 1987, was known as Black Monday during the 1987 global stock-market crash.
The Dow Jones Industrial Average dropped 508 points, or 22.6%, in a single session. That remains its largest one-day percentage decline, although later crashes produced larger point losses because the index was much higher in absolute terms.
Selling spread rapidly across international markets. Hong Kong fell first, followed by markets in Europe and the United States. Analysts have linked the episode to overvalued shares, rising interest rates, economic concerns, and computerized portfolio-insurance strategies that accelerated selling.
Black Monday did not lead to a depression comparable to the 1930s. The market eventually recovered, and regulators introduced measures such as circuit breakers to pause trading during extreme moves. The date is also used for other market crashes, so the year matters.