If something — like milk or a free shipping coupon — expires, it is no longer usable or valid. When you expire, you will be dead.
The verb expire comes from the Latin expirare, meaning “breathe out,” and the modern use retains that ancient meaning. The expanded, and more commonly used, meaning of expire is that the breath has — literally or figuratively — departed. When you expire your breath, you breathe out; you exhale. Things with a limited shelf life sometimes offer an expiration date that lets you know when they will expire: yogurt, frozen burritos, and even contracts for temporary employment. But some things expire in their own time: life, love, and car batteries.