What's the meaning of BA, SL, PU?

Hi, friends

When we post GI and if the stock is not enough, we always meet this kind of error message like "Deficit of BA..." , "Deficit of SL...", "Deficit of PU GR..." and so on.

I only know that it differs from different cases of stock type, but don't know what each abbreviation means.

Could anyone tell me what's the exact meaning of BA, SL, PU? And other abbreviations if there exist.

Wesley

Thanks!