How many of us have cleaned a cupboard, refrigerator or freezer and tried to remember when we bought a food buried in the back?In other words, it might refer to whether a commodity should no longer be on a pantry shelf (unfit for use), or just no longer on a supermarket shelf (unfit for sale, but not yet unfit for use).
The concept of expiration date is related but legally distinct in some jurisdictions.
Shelf life is the recommended maximum time for which products or fresh (harvested) produce can be stored, during which the defined quality of a specified proportion of the goods remains acceptable under expected (or specified) conditions of distribution, storage and display. High-acid canned foods (tomatoes, fruits) will keep their best quality for 12 to 18 months; low-acid canned foods (meats, vegetables) for 2 to 5 years. A product that has passed its shelf life might still be safe, but quality is no longer guaranteed.
For example, pasteurized milk can remain fresh for five days after its sell-by date if it is refrigerated properly.
However, improper storage of milk may result in bacterial contamination or spoilage before the expiration date.
It is often applied in shelf life estimation, sometimes wrongly.