October 29, 1929, is known as Black Tuesday, the worst trading day of the Wall Street Crash.
About 16 million shares changed hands on the New York Stock Exchange that day, overwhelming the exchange’s systems and producing enormous losses. The Dow Jones Industrial Average fell about 12%, following a 13% decline on Black Monday, October 28.
Black Tuesday did not by itself cause the entire Great Depression. The crash reflected earlier weaknesses, including excessive speculation, purchases made with borrowed money, falling industrial demand, and problems in the banking system. The market continued declining after October 1929 and did not reach its low until 1932.
A common mix-up is to call the whole 1929 event “Black Tuesday.” The broader episode is usually called the Wall Street Crash of 1929, while Black Tuesday specifically refers to October 29. Black Thursday refers to October 24, the first major panic day of the crash.