Expiration

"I'm sorry, that patient expired." I heard that last night as work as I was calling the floor to report something on a lab that was being done. It just sounds so funny when they're talking about a human life. To say that we expired. What does it mean? Are we like that spoiled milk in the back of the refrigerator that should have been thrown out weeks ago when it started smelling bad? Or maybe it's just my morbid curiosity or something but when they say that someone expired, it just makes me think, do we have a "Best if used by" date on our bodies?