B
Back order only if new item (book industry - not yet published only)
Item on back order due to unpublished status.
F
Factory ship
Ship directly from factory to purchaser.
N
No back order
Back order is unacceptable.
W
Warehouse ship
Ship directly from warehouse.
Y
Back order if out of stock
Acceptable to put on back order if out of stock.
ZZZ
Mutually defined
Self explanatory.