Backbone —- Main wireless link:
Let me create a simple draw for you:
Z————A—————-B—————-C————-D
From Z-A-B-C-D will be backbone if rest of links are going out from these nodes like branches of tree. You can say in a tree, a trunk is Backbone and branches are extension wireless link.
Backhaul means: In above diag, for D —-between Z to C will be back-haul link.