The expiration date for three types of standardized contracts: stock options, stock index futures, and index options. Expiration Friday occurs four times a year, on the third Friday in the last month of each quarter. Investors often unwind their positions on these contracts on or immediately before expiration Fridays, which leads to increased trading volume and price volatility on those days.
The Friday once each quarter when stock index futures, index options, and stock options simultaneously expire. Investors tend to close out positions in futures, options, and stocks on expiration Friday with the result being extremely volatile prices on this day. See also triple witching hour.