Black Thursday was the nickname for October 24, 1929, the trading day that began the most notorious phase of the Wall Street Crash.
The Dow Jones Industrial Average fell sharply that morning as heavy selling overwhelmed the New York Stock Exchange. A group of major bankers later met at J.P. Morgan & Co. and announced a plan to buy shares at prices intended to restore confidence. The market recovered much of its intraday loss, but the intervention did not end the crisis.
Selling returned on Black Monday, October 28, and intensified on Black Tuesday, October 29. Those later sessions made the collapse more dramatic, but Black Thursday is generally treated as the opening day of the famous late-October sequence.
The event is sometimes confused with Black Thursday in other historical contexts. In stock-market history, the phrase specifically refers to October 24, 1929, in New York.