LeeG: Thanks for the explanation of the terms and thanks everyone for your input and will look forward to others comments.

I guess I was sort of worried about my Specialized tires because they hardly have any tread and look like they would be really vulnerable to sharp rocks, etc., but I did take the bike up to a local park where there are a lot of dirt bike riders.. very serious riders. Anyway, I managed to get up to the top of a ridge with a friend and coming down I had to go really slowly because I have no suspension and am definitely not a dirt bike, also the trails are hard dirt with very sharp gravel/rocks covering them and I was amazed that I managed to survive with no problems and no sign of damage to the tires at all. I obviously won't try it again though.