triple witching hour

noun
  1. the last hour of trading on the New York Stock Exchange on the four Fridays each year when stock options, stock index futures, and options on such futures simultaneously expire: regarded as a time of extreme volatility in trading.

Origin of triple witching hour

First recorded in 1985–90
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018