Originally Posted by pablosnazzy

if it's paved, it's road riding. if it's dirt, it's mountain biking. the type of bike, size of path, etc, is irrelevant.

road biking stops and mountain biking starts when the pavement turns to dirt.

of course, you can get a bit more specific or fine tune it, such as:

lycra and snobbishnes = road riding, baggies and getting high = mountain biking.