Bills of lading have a number of additional attributes, such as on-board, received-for-shipment, clean, and foul. An on-board bill of lading denotes that merchandise has been physically loaded onto a shipping vessel, such as a freighter or cargo plane. A received-for-shipment bill of lading denotes that merchandise has been received, but is not guaranteed to have already been loaded onto a shipping vessel. Such bills can be converted upon being loaded. A clean bill of lading denotes that merchandise is in good condition upon being received by the shipping carrier, while a foul bill of lading denotes that merchandise has incurred damage prior to being received by the shipping carrier. Letters of credit usually will not allow for foul bills of lading.[2]