@ mattc
Matt, semantically, it's a moot point: it is not on roads, therefore it is off road, although traffic-free is also a fair description. I think off road is a perfectly satisfactory definintion in cycling terms, as we have "rough stuff" (and that has an honourable and ancient history in cycling) to describe the gnarlier stuff. But I'm not bothered really! I suppose it might become a talking point if this type of riding were ever to become an official sub (or super) section of rides. Certainly, "traffic-free" would represent a big attraction for many riders. Then again, experience shows that offering a ride that contains a lot of trails puts off people who are not used to having to wash their bikes!
Peter