Best before is often written on food wrappers, followed by a date, and is intended to indicate the date before which the supplier intended the food should be consumed. The term sell by is similarly used to indicate the date by which the item will have outlived its shelf life, and is intended to ensure that customers will not unwittingly purchase stale food. Sometimes the packaging process involves using pre-printed labels, making it impractical to write the best before date in a clearly visible location. In this case, a term like best before see bottom or best before see lid might be printed on the label and the date marked in a different location as indicated.
These terms have occasionally been criticised by literate people as being examples of poor usage of English, but the terms are now ubiquitous, usually well understood, and less verbose than grammatically correct alternatives.