The 29 October 1929 US stock-market collapse is commonly called Black Tuesday.
Black Tuesday was the fourth major selling session in late October 1929. About 16 million shares changed hands on the New York Stock Exchange, a record at the time, while the Dow Jones Industrial Average fell roughly 12%. The selling followed Black Thursday on 24 October and Black Monday on 28 October.
The crash did not single-handedly cause the Great Depression. It damaged confidence and wealth, but bank failures, falling production, deflation, reduced spending, and policy mistakes made the economic downturn far deeper. The US economy had already developed major imbalances, including heavy margin borrowing and speculative investment.
A common mix-up is treating Black Tuesday as the entire 1929 crash. It specifically refers to 29 October, whereas the Wall Street Crash of 1929 covers the broader sequence of market collapses. The Dow eventually reached a low in July 1932, nearly three years after Black Tuesday.