When I print a PO, what is the 'Part #' column ?

When you choose to print a purchase order within the purchase order details, there is a column on the PDF with 'Part #'. The part number column is going to pull from the 'Supplier SKU #' which can be set by clicking the binoculars next to a product in Inventory Management and the finding the Supplier section of the page, see below;

If the 'Supplier SKU #' is not set, the column for part number is going to be blank.