根据Cambridge Dictionary,

The expiration date means the last day on which a product or service can be used.

The expiry date means the date at which a document, agreement, etc. has no legal force or can no longer be used.

有效期限的英文可以用 expiration date 或是 expiry date，这边先来解释一下单字的部分，expiration 和 expiry 都是名词，中文意思皆为「到期、期满」，它们的动词型态为相同意思的 expire，其中 ex 为「向外」，pire 有「呼吸」之意，整体可以解释为「向外呼出最后一口气」，所以会有「结束、到期」的意思。

An expiration date is a date after which food is no longer safe to be eaten or sold. Expiration date might also apply to the point at which a contract or other agreement becomes invalid.

In America, expiration dates are not mandatory for most food products, and their use is not regulated at the federal level. Some products, like dairy, meat, and eggs, are regulated at the state level.

例句：

1.If you drink milk one day past its expiration date, you will probably not die.

2.I have a loaf of bread that expired four months ago, but it still smells fine and is not moldy, so I occasionally eat a piece of it as a challenge to the gods.

An expiry date is the date at which a product is no longer fit to be sold or eaten. It is primarily a British phrase. Unlike in America, expiry dates are mandatory for many products, and have been used since the 1970s.

那 expiration 和 expiry 的差别其实就在于 expiration 是美式英文，而 expiry 是英式英文，所以可以说它们是互相通用的，只是在不同地区选用的字会不同。

那不管是 expiration date 还是 expiry date，除了最常见的食品及药品的有效期限，还能用在租约、任期、信用卡等方面，也能称为「到期日、截止日」，也就是指过了这个日期后就会失去原有的效力了。

在搭配词上，「超过有效期限」可以说 pass the expiration/expiry date 或是 be past the expiration/expiry date，而「到期」可以说 reach the expiration/expiry date。

例句：

What is the expiration date of your credit card?

你那张信用卡什么时候到期？

expiration date 和 expiry date 在包装上常会缩写为 EXP 或是 EX，而日期的标示方式则会依照各国的习惯有所不同，通常包装上会注明年月日的顺序，以下举几个例子：

EXP: 10/23 有效期限为 2023 年 10 月

EX 18 OCT 23 有效期限为 2023 年 10 月 18 日