I guess it is all relative. I can't get home without climbing at least 400 feet. There are several roads up the hill to my home, but they all cover that elevation in about a mile. 400 feet in a mile is a good sized hill, but it is no mountain.

You need miles of climbing (and at least 100-200 feet of elevation gain per mile) before you can call something a mountain; anything else is either a steep hill or a not so steep hill.