There was a supermarket chain in Denmark, Irma, that would give you the item for free, if you found something in the store that was past the "sell by date". It is supposed to be sold before the "best by date" or the "use by date". That way the customer gets an item that still has some "shelf life". Best by dates are meant to indicate that the item will be at its best before that date. A "use by date" was probably invented by lawyers, to protect the company.