The October 24, 1929 U.S. stock-market crash day when panic selling began on the New York Stock Exchange was Black Thursday.
On that Thursday, a huge volume of sell orders overwhelmed the exchange and pushed prices sharply lower. A group of major bankers bought shares in an effort to restore confidence, and the market temporarily stabilized. That intervention did not end the broader collapse.
The crash continued through the following week. October 28 became known as Black Monday, and October 29 became Black Tuesday, when another wave of selling drove prices down dramatically. The 1929 crash is closely associated with the onset of the Great Depression, although economic contraction had multiple causes.
Black Thursday is sometimes used loosely for the entire 1929 crash, but its most specific meaning is the first major panic day, October 24. The name distinguishes it from the later Black Monday and Black Tuesday sessions.