Thanks.
As Pedro said, BUA stands for "Built Up Area", an area terrain feature in DBA common among Arable armies. You can model a BUA as a village, town or fortification such as a castle.
Cptain Blood:
Besides making 25mm trees and the occasional larger scale model for other people, I pretty much stick with 15mm, despite the best efforts of the Perry Brothers, Artizan, Gripping Beast, etc.
I did have a brief foray into 6mm sometime ago which was what actually got me interested in scratchbuilding.