The catastrophic New York Stock Exchange sell-off on October 29, 1929, is called Black Tuesday.
Black Tuesday followed Black Thursday, October 24, and Black Monday, October 28. On October 29, about 16 million shares changed hands, then an extraordinary volume for the exchange. Prices fell sharply as investors rushed to sell.
The crash did not single-handedly cause the Great Depression, but it helped destroy wealth and confidence. Banking failures, falling demand, debt problems, and policy mistakes deepened the economic collapse during the following years.
A common mix-up is treating Black Tuesday as the entire 1929 crash. It was the most famous day in a broader market collapse that began in September and continued into 1932, when the Dow Jones Industrial Average reached its low for the cycle.