A more thorough explanation:

An expiration date is the date on which an offer, option, or agreement comes to an end. It is the last day that the offer or agreement is valid.

For example, if a store offers a discount coupon that expires on December 31st, the coupon can no longer be used after that date. Similarly, if a lease agreement has an expiration date of June 30th, the tenant must vacate the property by that date.

Another example is a stock option that has an expiration date. If the option is not exercised by the expiration date, it becomes worthless.

These examples illustrate how an expiration date sets a deadline for a particular offer or agreement. Once the expiration date has passed, the offer or agreement is no longer valid.