A: TLDR: Food is good after the sell by date. How long it is good depends. If the product only has a “sell by” date, it is still good for some time if it is stored appropriately. (Eggs, for instance, if you put them in the fridge, maybe not in the door, can last more than a month past the sell by date). Goldfish are probably good for at least 3 months past the sell by date if unopened (in my experience). If opened and stored in some reasonable approximation of “closed” (air tight container, baggie, chip clip etc) I would say a 7—10 days. If opened and left opened, probably a day. You really can only tell for sure by looking at them/tasting them (I suppose you could try smelling too but I don’t imagine that would be helpful ;) For the record, most dry goods (like goldfish) will last far beyond a “best by” and even a “use by” date. (They maybe won’t taste quite the same but they are safe to eat)

A: Yes, it is a expatriation date on this line of products, according to my experiecnc​e.

A: Sell By is the last day the product should be in stores, and it should also be consumed before this date.