BPB (Baseplate Plus Brick) is a technique for raising, slightly, the ground level of your landscape. There are several advantages to this, mainly that lakes, rivers and streams can be placed lower than ground level for a much more natural look. It also opens up more opportunities for the use of bricks and plates that you otherwise might not be able to use in a flat landscape, since the basic ground level height is roughly one brick high (see here for example). All Base8 modules can be built without BPB, but there will be a noticeable discrepancy between baseplates. BPB can be achieved either by getting a hold of some 9.6mm (or roughly 3/8ths of an inch) thick material such as cardboard, foam-core or plywood and placing your baseplates on it, or you can build BPB supports. There are many ways to achieve this, see the following pictures for examples.
WAMALUG used BPB in October 2005 to recess the roads in their Fall for Fairfax castle display.