The frontier could be the export country's frontier, so it is important to specify where the relevant delivery point is. Seller bears all costs and risks up to that point. Seller bears all costs involved in transporting the goods. Buyer must clear the goods for import. Seller must deliver the goods to the wharf at the port of destination, cleared for importation.
Seller is responsible for all costs, taxes, duties and charges of delivering the goods.
Seller must deliver goods to the named destination and is responsible for all costs involved in transportation, including exportation. Buyer handles the import formalities. Same as DDU, however, the seller is responsible for import formalities as well. This represents the maximum obligation by the seller.