The 29 October 1929 trading day when U.S. stocks suffered massive selling was called Black Tuesday.
Black Tuesday followed Black Thursday on 24 October and Black Monday on 28 October. On 29 October, roughly 16 million shares changed hands on the New York Stock Exchange, a record at the time. Prices fell sharply as investors rushed to sell, and many buyers disappeared from the market.
The day is commonly treated as the symbolic climax of the Wall Street Crash, although the market continued to decline after October. The Dow Jones Industrial Average eventually reached a low in July 1932, far below its 1929 peak.
The crash did not by itself cause every feature of the Great Depression. Bank failures, falling demand, debt problems, protectionist policies, and monetary developments also contributed. Black Tuesday is therefore best understood as a dramatic market event within a much broader economic crisis.