the triple witching hour
noun[S]
STOCK MARKETinformalukuson astockmarket, the lasthouroftradingwhen threetypesofderivativescontractsend. Thesederivativesarestockindexfutures,indexoptions, andstockoptions:
TradersexpectadifficultdayonFridayas thetriplewitchinghourhitsthemarket.