One of many numbers you are given by your LRT (Laser Radio Terminal) when you scan the UPC on an item you'd like to know some information about.
This particular bit of info tells you how many of an item the store computers think you will get from the distributor at some later date.
It seems to be right every time I've checked it, though I've noticed the 'Delivery Date' (found in the 'Order Review' menu) for orders is sometimes wrong.
See also: Items On Hand, and Items In Transit.