The 24 October 1929 sell-off that helped trigger the Wall Street Crash was called Black Thursday.
On that day, heavy selling caused panic on the New York Stock Exchange, and the Dow Jones Industrial Average fell sharply. A group of major bankers attempted to restore confidence by buying prominent shares, temporarily calming the market.
The crisis continued despite that intervention. Black Monday followed on 28 October, and Black Tuesday came on 29 October, when trading volume and losses reached even more dramatic levels. The market then continued falling over the following months.
Black Thursday was not the entire crash, but it marked the first major panic session in the famous sequence. The economic effects extended beyond Wall Street and contributed to the broader Great Depression.