According to the Oxford English Living dictionary hiking is "The activity of going for long walks, especially across country."
To me a mile is quite a long walk around town although not a hike. I've done much longer walks but I'd call anything less than about a mile a short walk. It probably takes me longer to walk a mile than most of you though so to me it's a longer walk as it takes longer.
I just thought hikes were long walks in the great outdoors (or very long walks in urban areas) and by long I'd have thought anything that took a couple of hours or more.
Where do you draw the line? Do veteran hikers have a definition of it themselves? I'd be interested to see what hikers consider a hike.