Expiration dates on food packaging are intended to help stores and consumers determine the overall quality of a food item. Foods labeled with a "best if used by" date are considered at their highest quality when consumers use them by the expiration date, which is when quality begins degrading. The food is at its peak in flavor and quality before that date.
The "sell by" expiration date is a way manufacturers inform stores how long to display the item on store shelves. Items past their sell by date are often pulled from shelves over concerns about consistency in flavor, taste and freshness. Items that remain on shelves after this date are still edible for a period of time but may suffer some degradation that makes it less appealing to consumers. The "guaranteed fresh" date is placed on bakery items to indicate peak freshness. After this date, bakery goods might be stale.
Canned and packaged food items usually have a "pack" date in the form of a code. Some items have a month and year date. Manufacturers sometimes use Julian calendar-style dating on packaging. Beer cans and bottles may have a "born on" date, referring to its time of manufacturing. Many packaged foods remain good to consume one to several weeks after the expiration date.