The 1929 U.S. stock-market crash day when panic selling peaked on October 29 was called Black Tuesday.
Black Tuesday saw about 16 million shares traded on the New York Stock Exchange, a record at the time. The Dow Jones Industrial Average fell about 12%, following major declines on Black Thursday, October 24, and Black Monday, October 28.
The crash did not single-handedly cause the Great Depression. It exposed severe weaknesses, including speculative buying with borrowed money, overvalued shares, falling industrial production, and fragile banks. The wider economic downturn developed through the early 1930s.
A common mix-up is treating Black Tuesday as the entire crash. Historians generally describe the October 1929 collapse as a sequence of trading disasters, while Black Tuesday is the best-known single session. The Dow eventually lost almost 89% from its September 1929 peak to its 1932 low.