Dwain Harrison- the definition of myth

In the beginning of the year in this class, we discussed the word "myth". This word has troubled me and has definitely confused me. The defintion of myth from a dictionary is "a widely accepted but false idea". However, we discussed that this was not the case. Myth is actually something that is unattainable in a human aspect. That is, we cannot understand because we have not seen its beginning or its end. This, however, goes against what I have been taught in school all of my life up until this point. I have usually associated the word myth with "Greek mythology" like Zeus and Medusa, not with Christianity. So, this idea does confuse me but this is not the first time I have heard someone use the word myth for Christianity. I am not quite sure but I will definitely do some more research in order to find out more about it.