What term describes the sudden U.S. market plunge on May 6, 2010, when major indexes briefly lost about 9%?

The sudden U.S. market plunge on May 6, 2010, was the Flash Crash of 2010.

During the afternoon of May 6, major U.S. equity indexes fell rapidly and then recovered much of the loss within minutes. The Dow Jones Industrial Average briefly lost nearly 1,000 points, while the S&P 500 and Nasdaq also experienced abrupt declines.

Investigations found that automated trading, market fragmentation, and rapidly changing liquidity played important roles. The U.S. Commodity Futures Trading Commission and Securities and Exchange Commission later concluded that a large sell order and high-frequency trading activity helped amplify the move.

The crash did not represent a normal, months-long bear market like 1929 or 1973–1974. Its defining feature was the extraordinary speed of the decline and partial recovery. Regulators subsequently introduced measures including circuit breakers and a ban on clearly erroneous trades.