Grandfather clause表示“祖父条款”。

Black’s Law Dictionary Ninth Edition对该条款共有四条定义：

“1. A clause in the constitutions of some Southern states exempting from suffrage restrictions the descendants of men who could vote before the Civil War; 2. A provision that creates an exemption from the law’s effective date; specif., a statutory or regulatory clause that exempts a class of persons or transactions because of circumstances existing before the new rule or regulation takes effect; 3. In a government contract, a provision that immunizes the contractor against any changes in federal law that would otherwise adversely affect the contract; 4. In a construction contract, a general and inclusive provision that makes a party responsible for dealing with risks, whether expected or unexpected.”

针对前两项定义，《元照英美法词典》给出了解释：

“1. 法律、法规中的不回溯条款或例外条款。新的法律、法规中规定的某些限制，不适用于已经开始的活动，并允许其继续进行。《机动车运输业法》（Motor Carrier Act）中的‘祖父条款’规定，凡在本法通过前已经建立的运输机构可以继续经营。2. 南方一些州的宪法规定，凡1867年前享有选举权的人，或内战时期服役于联邦陆、海军或邦联军队的人，以及上述两类人的合法后裔，不受财产状况和读写能力的限制，一律享有选举权。1915年美国最高法院宣布此项条款为违宪。”

实际上，《关贸总协定》（GATT）的《临时适用议定书》中就有“祖父条款”，其中规定：在不违反现行立法的前提下，最大限度的适用《关贸总协定》的第二部分。

基本含义：

1. A clause in the constitutions of some Southern states exempting from suffrage restrictions the descendants of men who could vote before the Civil War. The U.S. Supreme Court held that a clause of this kind in the Oklahoma Constitution violated the 15th Amendment. 

1. 美国南部一些州的宪法中的一项条款规定，在南北战争之前可以投票的人的后代不受选举权限制。后美国最高法院裁定，《俄克拉荷马州宪法》中的此类条款违反了宪法第15修正案。

2. A provision that creates an exemption from the law's effect for something that existed before the law's effective date; specifically, a statutory or regulatory clause that exempts a class of persons or transactions because of circumstances existing before the new rule or regulation takes effect. 

2.对法律生效日期之前存在的东西免于法律效力的规定；尤其指对在新法律或法规生效之前就存在的情形，规定某类人员或交易免于法律效力。

3. In a government contract, a provision that immunizes the contractor against any changes in federal law that would otherwise adversely affect the contract. 

3.政府合同中的一项规定，可以使缔约人免于联邦法律的任何变更，否则可能会对合同产生不利影响。

4. In a construction contract, a general and inclusive provision that makes a party responsible for dealing with risks, whether expected or unexpected.

4.在建筑合同中，一项一般性包容性的条款，使一方对应对（无论预期还是意外的）风险负责。

例句一

A grandfather clause (or grandfather policy) is a provision in which an old rule continues to apply to some existing situations while a new rule will apply to all future cases.

祖父条款（或祖父政策）是一种规定，指旧规则继续适用于现有情况，而新规则将适用于将来的所有情况。

例句二

For example, a “grandfathered power plant” might be exempt from new, more restrictive pollution laws, but the exception may be revoked and the new rules would apply if the plant were expanded.

比如，一座“祖父条款下的发电厂”可以免于新的、约束力更强的污染法限制，但是一旦发电厂扩建，该例外就会失效，新的法律将适用。