October 29, 1929, the climax of the Wall Street Crash, is most commonly called Black Tuesday.
On that day, about 16 million shares changed hands on the New York Stock Exchange, setting a trading-volume record that stood for decades. Prices plunged as investors rushed to sell, following major losses on Black Thursday, October 24, and Black Monday, October 28. The collapse destroyed enormous amounts of paper wealth.
The crash followed a period of rapid speculation during the 1920s. Many buyers purchased shares with borrowed money, while stock prices rose far faster than corporate earnings in several sectors. When confidence weakened, margin calls forced investors to sell, adding pressure to already falling prices.
Black Tuesday did not by itself create the entire Great Depression. Banking failures, reduced consumer demand, falling industrial production, deflation, and policy mistakes also mattered. The crash is nevertheless remembered as the clearest symbolic turning point from the prosperity of the 1920s to the severe economic contraction that followed.