What was the name of the catastrophic 1929 U.S. stock-market collapse that helped begin the Great Depression?

The catastrophic 1929 U.S. stock-market collapse was the Wall Street Crash of 1929.

After years of rapid share-price growth and widespread buying on margin, confidence weakened in autumn 1929. Prices fell sharply on October 24, often called Black Thursday, and selling intensified on October 28 and October 29, known as Black Monday and Black Tuesday. The Dow Jones Industrial Average lost nearly 23% over those two October days.

The crash damaged banks, businesses, and household wealth, but it was not by itself the entire cause of the Great Depression. Bank failures, falling demand, debt, deflation, and policy choices deepened the economic collapse. A common mix-up is treating Black Tuesday as the name of the whole event; it refers specifically to October 29, while the broader episode is the Wall Street Crash of 1929. The Dow did not regain its September 1929 peak until 1954.