October 29, 1929, was known as Black Tuesday during the Wall Street Crash.
The Dow Jones Industrial Average fell 11.7% that day, as roughly 16 million shares changed hands. The selling followed major declines on Black Thursday, October 24, and Black Monday, October 28.
Black Tuesday is often treated as the symbolic climax of the crash, but the collapse unfolded over several trading sessions. The Dow had peaked in September 1929 and continued falling for years afterward, reaching its low in July 1932.
The crash did not by itself cause the entire Great Depression, although it damaged confidence, reduced wealth, and intensified broader economic problems. A common mix-up is calling October 24 Black Tuesday; that date is Black Thursday.