The day on which any four classes of option contracts (stock index futures, stock index options, stock options and single stock futures) expire. This day falls on the third Friday of March, June, September and December. On this day, derivative traders exercise their in the money options and take delivery on their futures contracts. Likewise, on this day arbitrageurs make their arbitrage transactions concerning the above classes of contracts. This day is one of the most turbulent and heavily traded days of the year.

It is also known as quad witching day.