29 October 1929, the most infamous day of the Wall Street Crash, is known as Black Tuesday.
On that day, investors traded roughly 16 million shares on the New York Stock Exchange, a record at the time. The Dow Jones Industrial Average fell about 12%, following a sharp decline on Black Monday, 28 October. The selling reflected years of speculation, widespread purchases on margin, weakening economic conditions, and growing fears that share prices had risen too far.
Black Tuesday did not cause the entire crash by itself. It was one of several devastating sessions in October 1929, and the market continued falling afterward. The Dow eventually reached its low in July 1932, losing nearly 89% from its September 1929 peak.
A common mix-up is confusing Black Tuesday with Black Thursday, the earlier 24 October sell-off, or Black Monday in 1987. These names refer to different market crises.