Item type is used on the order and invoice to indicate the kind of processing and the default account code used on the generated invoice for posting.

The default list:

itemTypeIddefault account Codedirection(in/out/either)
ItemExpenseoperating expenseeither
ItemProductunreceived inventoryin
ItemProductproduct salesout
ItemRentalasset rental salesout
ItemSalessales revenueout
ItemSalescost of salesin
ItemSalesTaxsales tax collectedout
ItemSalesTaxsales and use taxesin
ItemServiceProductservice salesout
ItemShippingcost of sales freightin
ItemShippingshipping fees receivedout
ItemVatTaxVAT collectedin
ItemVatTaxVAT usedout