29 October 1929 became known as Black Tuesday after heavy selling drove U.S. share prices sharply lower.
Black Tuesday followed Black Thursday on 24 October and Black Monday on 28 October. On 29 October, roughly 16 million shares changed hands on the New York Stock Exchange, a record at the time. The Dow Jones Industrial Average lost about 12% that day.
The crash ended the speculative boom of the 1920s, when many investors had bought shares with borrowed money. Falling prices forced leveraged investors to sell, creating additional pressure. The market collapse was a major event in the onset of the Great Depression, although the depression also involved bank failures, falling demand, deflation, and policy decisions.
The crash did not consist of one single day. Prices continued falling after October 1929, and the Dow reached its major low in July 1932. That longer decline is why the broader episode is better described as the Wall Street Crash rather than simply Black Tuesday.