Basically, its using old roads/tracks that are no longer used by general traffic. It can vary from being a single track a few feet wide, to wide rocky trails, through streams, rivers, woods, etc and often VERY deep mud as we found out again a few weeks ago. Excellent fun if you have a route planned out and dont know what to expect. But as i said you need to be FULLy road legal as they are still classed as 'roads'.