October 29, 1929, the most famous day of the Wall Street Crash, is known as Black Tuesday.
On that day, investors sold roughly 16 million shares on the New York Stock Exchange, overwhelming the market and helping intensify the crash that had begun days earlier. The Dow Jones Industrial Average fell about 12%, following a decline of roughly 13% on Black Monday, October 28.
The crash did not single-handedly cause the Great Depression, but it severely damaged confidence, reduced wealth, and contributed to a broader economic contraction. Falling bank lending, business failures, and high unemployment followed in the United States and elsewhere.
A common mix-up is Black Thursday, October 24, the first dramatic selling day of the episode. Black Tuesday specifically refers to October 29, while Black Monday refers to October 28.