What was the name of the brief 6 May 2010 U.S. market plunge?

The brief U.S. market plunge on 6 May 2010 was the Flash Crash.

During the afternoon of 6 May 2010, major U.S. equity indexes fell rapidly and then recovered much of the loss within minutes. The Dow Jones Industrial Average dropped about 1,000 points, or roughly 9%, before rebounding. Prices in individual stocks and exchange-traded products became temporarily dislocated, with some trades executing at extremely low or high prices.

Investigations concluded that automated trading and a large sell order interacted with fragile market liquidity. The exact legal and technical history involved several participants and later enforcement actions, so the event is better understood as a complex market-structure failure than as one simple human error.

The Flash Crash differs from Black Monday in 1987 and the 1929 crash. It was exceptionally fast and largely intraday, while those earlier crashes involved sustained market declines over longer periods. New trading safeguards were introduced afterward.