Options have expiration dates that differ according to the underlying asset. Stock options expire on the third Friday of the month. Futures options expire on different days depending on the contract. Sometimes, different options classes expire on the same day. These days, depending on the scenario, may be referred to as double-, triple-, or quadruple-witching days.
Double-witching days refers to the scenario where any two of the different classes of options expire. The classes of options may refer to stock, stock index, or stock index futures options.