29 October 1929 was called Black Tuesday, the day a massive wave of selling intensified the Wall Street Crash.
On Black Tuesday, roughly 16 million shares changed hands on the New York Stock Exchange, a record at the time. The Dow Jones Industrial Average fell nearly 12%, following major declines on Black Thursday, 24 October, and Black Monday, 28 October. Investors had bought heavily on margin during the 1920s, so falling prices triggered forced sales and worsened the downward spiral.
Black Tuesday is a key date in the broader 1929 crash, not the sole beginning of the event. The collapse damaged banks, businesses and household wealth, while the subsequent economic contraction became the Great Depression. The crash itself was not the only cause of the Depression; bank failures, reduced demand and policy choices also contributed.