I found these definitions at answers.com:

Hill: A well-defined natural elevation smaller than a mountain.

Mountain: A natural elevation of the earth's surface having considerable mass, generally steep sides, and a height greater than that of a hill.

Either one of these makes me wonder where those invisible hills my legs keep finding fit in!

When searching google for "hill versus mountain" I found this article discussing the issue: http://www.mtnforum.org/rs/bulletins...in-2001-09.pdf

I still don't know!

Karen in Boise