fill or kill order
noun[C]
STOCK MARKETukus(abbreviationFOK)aninstructionto abroker(= someone whobuysandsellsshares, etc. for otherpeople)tobuyorsellparticularstocksorsharesimmediately:
Butunlikeafillorkillorder, it isn'tcancelledif it's notexecutedimmediately.