The 24 October 1929 sell-off that began the Wall Street Crash is commonly called Black Thursday.
On that Thursday, panic selling overwhelmed the New York Stock Exchange. Trading volume reached a then-record level, and the Dow Jones Industrial Average fell sharply. A group of major bankers bought heavily near the end of the session, helping stabilize prices temporarily.
The apparent recovery did not end the crisis. Selling returned on the following Monday and intensified on Tuesday, 29 October, which became known as Black Tuesday. The wider Wall Street Crash continued after those dramatic sessions and contributed to the economic collapse known as the Great Depression.
Black Thursday is sometimes confused with Black Tuesday because both dates are central to the 1929 crash. The Thursday label specifically identifies the first major panic day, not the final and most notorious selling session.