The seller delivers the goods to the buyer, not cleared for import, and not unloaded from any means of transport at the named place of destination. The seller has to bear the costs and risks involved in bringing the goods thereto, other than, where applicable, any 'duty'. Duty refers to any customs formalities, payment for such, customs duties, taxes and any other charges for import in the country of destination. Such duty has to be borne by the buyer as well as any costs and risks incurred by his failure to clear the goods for import in time.
These costs can be borne by the seller if explicitly stated in the contract.
DDU can be used for any mode of transport but when delivery is to take place in a port of destination on board a vessel or on the quay (wharf), the DES or DEQ terms should be used.