My wife asked me how far I was going out tonight. I told her around 5 miles. She said, "You are a doing a long run tonight.". I thought about for a moment and realized, that this was a medium length run.
There was a time when 5 miles was my long run and if I pushed it, maybe I could do 6. 3 was my standard run with the occasional 4 mile run mixed in.
Now, my short runs are 3 and 4 miles. My medium runs are 5, 6, 7 and my long runs are 8, 9 and above. I have come a long way over the years.