The 1929 New York stock-market crash day when the Dow fell about 12.8% was called Black Monday. It occurred on October 28, 1929, during a week of extreme selling on the New York Stock Exchange.
Black Monday followed a sharp decline on the preceding Thursday and came before Black Tuesday, October 29. The Dow’s fall on October 28 was about 38.33 points, a large percentage move for the period. Panic selling continued as investors rushed to liquidate shares bought with borrowed money.
The crash did not by itself cause every feature of the Great Depression, but it became its most famous financial symbol. Weak banks, reduced demand, falling investment, and international economic problems deepened the downturn. A common mix-up is calling October 28 Black Tuesday; Black Tuesday refers specifically to October 29.