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| Term | Meaning |
| Ocean Waybill | A document, issued by a shipping line to a shipper which serves as a receipt for the goods and evidence of the contract carriage. |
| Off-hire Clause | In a time charter, the owner is entitled to a limited time for his vessel to be off hire until such time as the vessel may be repaired or dry-docked. |
| Off-load | Discharge of cargo from a ship. |
| Open Rates | Pricing systems that are flexible and not subject to conference approval. Usually applied to products in which tramps are substituted for liners. |
| Open Registry | A term used in place of "flag of convenience" or "flag of necessity" to denote registry in a country which offers favorable tax, regulatory, and other incentives to ship owners from other nations. |
| Open Top Container | A container fitted with a solid removable roof, or with a tarpaulin roof so the container can be loaded or unloaded from the top. |
| Overtonnaging | A situation where there are too many ships generally or in a particular trade for the level of available cargoes. |