Though some manufacturers may interpret it as the date the product was packed in the retail packaging in which it will be sold at retail to consumers; some may interpret as the date in which these packaged goods were further packed for shipping to the retailer.
Usually it is a cryptic date code, rather than something given as a plain English date that is immediately understandable. It’s more for manufacturer’s tracing purposes, than yours for interpreting freshness.
Sometimes, the code for a day may be that day’s number in a year (e.g. December 31st, being the 365th day in a year, would be coded as 365; 27th January would be coded as 027.) But there is no standard, nothing that says the code even has to relate to the calendar, let alone the Gregorian calendar that we now use.
Such dates are usually used on tinned, box and bagged goods.
In America, since 1972, The Food Safety and Inspection Service (FSIS) has required poultry to have either a date of packing OR a sell-by or use-by date. The poultry packaging doesn’t have to be a plain calendar date that consumers can read, however: it can be a code, but if a sell-by or use-by date is supplied instead, then it must be in plain calendar format.
In Canada, a Packaged-On Date is required on meat, and on any perishable goods with a lifespan of under 90 days packed right at stores.