double-lasted*

The AR8 is a boot model. Double lasted means those models have two layers of leather instead of one - they are fully leather lined, and together at least about 4mm of leather thickness anywhere. These are also even more water resistant. Ar8, razorback and the stockman are double lasted for sure, don't know about most other models.

Single lasted stitchdown is very basic - one layer of leather, curved outwards and stitched down to the midsole, with the rubber (outsole) glued on the bottom.

Double lasted - the outer layer is curved outwards and the inner kayer is curved inwards. That's also what gives more water resistance....