FSB Wall, the highest FSB your motherboard can handle. You can run total speed less than what your system will perform at, but at the max FSB. So maybe your system will do 525 FSB (6x525-3.15), even though it may run faster (8x400=3.4) So 525 is the wall.
FSB Hole. Motherboards use dividers Some motherboards won't post or run at all at certain speeds. Example: your motherboard won;t work between 380 and 400, but works fine at 401-480, or below 380.