Nubuck leather is very similar to suede, but with a very distinctive difference. Both have been sanded to give them a soft feel. The difference is that Nubuck leather is sanded on the inside part of the leather, whereas suede is sanded on the outside. You can find more information here: http://www.wisegeek.com/what-is-nubuck.htm
Nubuck is a type of high quality rawhide leather that is sanded to acheive a bit of a nap. This creates a velvety like texture, that is similar to suede. Cowboys like it because it is wear resistant and lightweight.