what is luck??

I was wondering what is luck??? when is a student said to be lucky???
Well being a student i was thinking when can a student feel he is lucky. Most of the time its the exams that seem to decide the fate of the student. So if a student does well in the exam does it mean that he is lucky??? well I don't know if there is anything called as luck.

A student doing well in the exams implies that "he did a good preparation for the exams" and "the exam paper had question from topics that he covered well". I don't see any role of luck in the first part of the statement but the second part of the statement can just be a coincidence of his intuition and his alertness in class, for your intuition to help you decide what to leave out requires knowledge about the portion for the exams and your ability to decide how important a topic is compared to other. If a student can decide how important a topic is compared to other topics he already has enough insight about the subject and deserve a better grade.

So is a person called lucky if he banked on his intuition and it turns out to be correct, i guess at least in the the case of student its hard to find the role of luck in the success.