The 1929 New York Stock Exchange crash day when the Dow fell nearly 12% was Black Tuesday.
Black Tuesday occurred on 29 October 1929, after heavy selling had already shaken the market on Black Thursday and Black Monday. About 16 million shares changed hands, a record at the time, and the Dow Jones Industrial Average lost approximately 12% in one day.
The crash did not by itself create every feature of the Great Depression, but it became its best-known financial symbol. Economic contraction, bank failures, falling production, unemployment, debt, and international monetary problems all helped deepen the depression that followed.
A common mistake is to treat Black Tuesday as the first day of the 1929 crash. It was the climactic selling session, not the beginning. Another mix-up is confusing the 1929 event with Black Monday in 1987, when the Dow experienced a much larger percentage decline in a single day.