在“open cover”和“open policy”中，“open”均指“预约”。

open cover预约保险。保险公司与被保险人之间的货运保险合约的一种，其主要内容是：在双方约定的期限内，被保险人一切装运出口货物按约定的费率自动地得到保险。货物装运后，被保险人应立即通知保险人，由保险人签发保险单。被保险人先预缴一定金额的保险费，在货物价值确定以后再做调整。

Open cover is a type of marine insurance policy in which the insurer agrees to provide coverage for all cargo shipped during the policy period. Open cover insurance is most commonly purchased by companies that make frequent shipments, as the blanket coverage keeps them from having to purchase a new policy each time a shipment is made.

open policy预约保险单。指根据预约保险协议签发的保险单。预约保险单仅对货物保险的一般条件和总的金额、保险期限做约定，每票货物启运时，被保险人仍需对保险人履行保险人宣告义务。A marine cargo open policy is the agreement between a merchant and an insurance company to insure all goods in transit falling within that agreement for an agreed period or even indefinitely until the agreement is cancelled by either party. ... The countries or places to or from which the goods will be insured.

它们之间的区别在于预约保险单已加盖公章因此可强制执行，而预约保险并未加盖公章，因此并无法律效力，但其有加盖公章的保单/保险证书佐证的除外。

The open policy differs from an open cover in certain important respects. They are : (a) The open policy is a stamped document and is, therefore, legally enforceable in itself, whereas an open cover is unstamped and has no legal validity unless backed by a stamped policy/certificate of insurance.

海运贸易中关于“open”常见的搭配如下：

first open water/FOW解冻后即起航。 用于冬季冰冻的北方港口的租船合同，意指解冻后立即起航。

open letter of credit光票信用证；无限定条件信用证；开口信用证。信用证的一种，不需要随附权利凭证〔documentary title〕，只需凭汇票即可付款的信用证。

open price待定价格；(合同成立时)未确定价格。特别适用于货物买卖中，指货物买卖合同成立时尚未确定价格。根据美国《统一商法典》〔U.C.C.〕第2-305条关于待定价格条款的规定，只要当事人确有订立买卖合同的意图，即使售价未确定，合同仍可以成立；在此情况下，合同价格应为交货时的合理价格。与此相对的是约定价格〔agreed price〕。