What nickname was given to the extreme US market sell-off on 6 May 2010?

The extreme US market sell-off on 6 May 2010 was called the Flash Crash.

During the afternoon of 6 May, major US equity indexes fell rapidly and then recovered much of the loss within minutes. The Dow Jones Industrial Average briefly lost nearly 1,000 points, one of its largest intraday point declines at that time. Some individual securities traded at wildly abnormal prices before normal conditions returned.

Investigations linked the episode to interactions among high-frequency trading, automated orders, and a large sell order in an already nervous market. The event showed that electronic markets could move far faster than human traders could assess events. Later changes included tighter controls, trading pauses, and mechanisms for reviewing clearly erroneous trades.

The Flash Crash was not a conventional multi-year bear market. Its defining feature was the extraordinary speed of the fall and partial rebound. A separate 2010 report identified trader Navinder Singh Sarao as a participant whose spoofing activity contributed to the episode.