Good fortune or a happy outcome, especially by chance. For example, It was sheer good luck that brought this offer my way, or, as Shakespeare put it in The Merry Wives of Windsor (3:5): "As good luck would have it, comes in one Mistress Page." [Late 1400s]
Also, good luck to you. I wish you success. This term is used both straightforwardly, as in Good luck on your journey, and sarcastically, implying that what someone is undertaking is not likely to succeed, as in If you think you'll find that long-lost letter, good luck to you.