Well it sort of depends. I once asked a professor this question and he responded with, "it blows up, like a bomb."
One way I like to think of it is in a real context. First of all lets say I had no hamburgers and five friends, and I wanted to share my hamburgers with my friends. since there are six of us this is 0/6. The question, then, is how much food do each of my friends get? None of course because there is no food! Now we flip the script. Lets say i have six burgers but i have not friends to share them with. How many burgers do each of my friends get? Mathematically this looks like 6/0 and at first many people think this is also zero. Consider it more closely though, the question was how many burgers do each of my friends get? Since I have no friends in this context it the question makes no sense and therefore we cannot answer the questions. When we run into things like this in math we say they are undefined.
another answer to this is infinity. Pick a number, any number and divide it by 1. Then divide by .5, then by .2 then .1. Divide it by .01 and .001 and .0001 and notice the pattern. The numbers get massive! This is undoubtedly what my professor meant when he said it blows up like a bomb!