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 items the store computers think you have in the store.
At the store where I work, it is not infrequent that this number is off by at least a bit.. every once in a while it's off by great deal. (Example: on July 7th, Zellers #148 had -392 bottles of diet coke, which I can only assume was due to someone giving Zellers just under 400 bottles of the stuff 'off the books'.. you know.. the Soda Black Market)
Also see: Items In Transit, and Items On Order.