The 1929 trading day known as Black Tuesday was 29 October 1929.
Black Tuesday followed Black Thursday, 24 October, and Black Monday, 28 October. On 29 October, about 16 million shares changed hands on the New York Stock Exchange, setting a trading-volume record that lasted for decades. Prices fell sharply as investors rushed to sell, and the Dow Jones Industrial Average lost nearly 12% that day.
The crash did not cause the entire Great Depression by itself. The economic downturn developed through several interacting problems, including bank failures, falling demand, debt, and declining industrial production. The market collapse nevertheless became its best-known financial symbol.
A common mix-up is treating Black Tuesday as the name of the whole crash. “Black Tuesday” specifically identifies the trading day, while the broader event is usually called the Wall Street Crash of 1929. Black Thursday and Black Monday were earlier panic days in the same episode.