So I was telling some people in the office about the 5k marathon I completed last weekend and one person said that his young son had just completed a fun run marathon. Turns out the fun run was only a mile. I told him that a real marathon has to be at least as long as what is referred to as a 5k. He got a little bit angry. So, who is right? Can a fun run be called a marathon, or do you have to run the full “5k” to be considered a marathoner?