An item that does not have inventory in the system, such as freight, is referred to as nonstock. The stock check box is not checked for these items. These items are added to purchase orders like a stock item but do not get received, do not create inventory, and do not go on the company ledger as inventory.

In addition to freight, this can be used for any purchase on a purchase order that needs to be tracked.  

Please also see the Accounts Payable document about processing the payable invoice for these items.