What was the nickname of the 1929 New York market collapse day on October 24?

The nickname of the 1929 New York market collapse day on October 24 was Black Thursday.

On October 24, 1929, heavy selling hit the New York Stock Exchange. The Dow Jones Industrial Average fell sharply in the morning, but a group of major bankers bought large blocks of shares in an attempt to restore confidence and support prices.

The intervention produced a temporary recovery, but it did not end the underlying market weakness. Selling returned on the following Monday and reached an even more dramatic scale on Black Tuesday, October 29.

Black Thursday is therefore one stage of the Wall Street Crash of 1929, not a separate financial crisis. The crash followed years of rising stock prices, widespread speculation, and purchases made with borrowed money.