With the exception of baby formula, there are no federal regulations on date labeling. Often the “best if used by,” “sell by,” and “use by” or EXP Date designations are just a manufacturer's best guess about how long their food will taste its freshest. Supermarkets may also use the dates as a guide when stocking shelves.
The dates have little to do with how safe the food is.
Sell By. This is the date set by manufacturers to tell retailers when to remove a product from shelves. The goal is to ensure that consumers have products at their best quality, which can be several days to several weeks, depending on the item. For instance, milk, assuming proper refrigeration, should last five to seven days past its sell-by date before turning sour.