From Longman Dictionary of Contemporary Englishgood luckgood luckused to say that you hope that someone is successful or that something good happens to them Good luck in your exams. → good
Examples from the Corpus
good luck• Mac users are wishing Steve Jobs and company good luck.• Why does a black cat bring good luck?• I want to know about good luck and bad luck.• Those for Diem were red, which signified good luck, and those for Bao Dai green, the color of misfortune.• I sometimes could not believe my good luck, and was grateful for it.• There's been good luck though, for Steve Bennett of Ross on Wye.• If they start talking high teens, good luck to them.• And finally good luck to Woodstock-based football manager Jim Smith the on Sunday. 