"Shelf life" has a few meanings....in grocery stores and supermarkets, certain products are perishable, and have a limited amount of time that they can be set out on display for consumers to purchase. We say that they have a short "shelf life."
In publishing, "shelf life" refers to book stores. Each store has a limited amount of display space, and certain areas (for example, near the front of the store, on an aisle, etc) are more coveted than others. If a title sells well, the store will keep it on a prominent shelf, or display area. Once the sales slow down, though, the book will be removed and placed in a less desirable area, or perhaps completely removed from display. The amount of time a book can remain out on display is referred to as its "shelf life."
Other types of media (video tapes, magazines, audio tape) have differing requirements when it comes to preserving them. Video tapes placed upright like books on a shelf are said to last longer than if they are stacked in a flat, horizontal position. They also have to be kept away from magnetized items (like stereo speakers) and light and dust. All of these factors determine their "shelf life" - how long they'll remain in viewable condition. Magazines, newspapers and reference books are increasingly being transcribed onto CDs or DVDs for storage purposes, as the original hard copies do deteriorate over time (sunlight, human handling, etc) and it takes much less shelf space to store a series of small disks versus the original paper copies.
Sorry this was so long, I hope it made some sense.
Shelf Life 
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