Food items you buy at the grocery store have dates on them, but that does not mean that the food expires on that date. What the date really does mean can vary depending on the food, the state, and exactly how it's worded. Stores use sell-by dates so they can make sure they're rotating their stock properly -to sell the oldest stuff first so nothing is wasted. Speaking of waste, you may be wasting food if you are convinced it goes bad by the date on the package.
Adam Conover of Adam Ruins Everything has the lowdown on how expiration dates work in the real world. And spoiled milk, which is a little icky. -via Tastefully Offensive