During the 1929 Wall Street Crash, the panic-selling peak occurred on Black Tuesday.
Black Tuesday was October 29, 1929, when investors sold roughly 16 million shares on the New York Stock Exchange. The enormous volume overwhelmed buyers and accelerated the collapse that had begun days earlier. The Dow Jones Industrial Average fell about 12% that day, following a similarly severe decline on Black Monday.
The crash did not by itself cause the entire Great Depression, but it became its most famous financial symbol. Weak bank regulation, speculative buying on margin, falling industrial production, and overextended businesses all contributed to the wider economic crisis.
A common mix-up is Black Thursday, October 24, the first major panic day, and Black Monday, October 28. Black Tuesday is specifically October 29, the day most strongly associated with the climax of the 1929 market collapse.