最近答主关注美国堕胎权，也看到了trigger law这个词汇，查到了trigger law的起源。

Trigger law is an informal term—it’s not used in an official way. The word trigger is used in the sense meaning “anything, as an act or event, that serves as a stimulus and initiates or precipitates a reaction or series of reactions.” In other words, a trigger law is a law that only goes into effect when a particular condition “triggers” it.

Laws considered trigger laws existed long before the term came to be commonly used. For example, two years after Roe v. Wade, Illinois passed the Illinois Abortion Law of 1975, which stated that abortion would be illegal in the state if Roe v. Wade were ever overturned in the future. (That 1975 law was repealed in 2017—it did not take effect due to the overturning of Roe v. Wade.)

The term trigger law started to become commonly used during the late 2010s and early 2020s. Before and after Roe v. Wade was overturned, the term was often used discussion of abortion access and how state laws would change (or go into effect) after the ruling.

关于trigger law的中文表达，虽然不少文章将其翻译为“触发法”（如下图），但是答主并未找到“触发法”的相关释义，欢迎讨论。

另附Wikipedia对trigger law的定义：

A trigger law is a law that is unenforceable but may achieve enforceability if a key change in circumstances occurs.

美国除了堕胎权事件外，在医疗救助计划事件中，也曾使用过trigger law一词，下文供参考：

The Affordable Care Act allowed states to opt in to a program of health care expansion, which allowed more residents to qualify for Medicaid. The cost of this expansion was primarily borne by the federal government, but the percent paid by the federal government was scheduled to decrease each year, reaching 95% by 2017 and below 90% by 2021; the remainder would be assumed by the state. As of 2017, eight states had laws that would trigger an end to participation in Medicaid expansion, if federal funding fell below a particular level. [needs update] Unlike abortion trigger laws prior to the overturning of Roe v. Wade, these are not unconstitutional at the moment and are only inactive because they rely on certain conditions to activate.