What do the expiration dates on foods really mean?

My mom sent me this article the other day, and I thought it would be interesting info to share.

"Which five foods are most often feared as being unsafe after the printed date? According to ShelfLifeAdvice.com, we are most wary of milk, cottage cheese, mayonnaise, yogurt, and eggs, and the site offers these helpful explanations:

Milk: If properly refrigerated, milk will remain safe, nutritious, and tasty for about a week after the sell-by date and will probably be safe to drink longer than that, though there’s a decline in nutritional value and taste.

Cottage cheese: Pasteurized cottage cheese lasts for 10-14 days after the date on the carton.

Mayonnaise: Unopened, refrigerated Kraft mayonnaise can be kept for 30 days after its expiration date or 3-4 months after opening, the company told ShelfLifeAdvice.

Yogurt: Yogurt will remain good 7-10 days after its sell-by date.

Eggs: Properly refrigerated eggs should last at least 3-5 weeks after the sell-by date, according to Professor Joe Regenstein, a food scientist at Cornell University. Note: Use of either a sell-by or expiration (EXP) date is not federally required, but may be state required, as defined by the egg laws in the state where the eggs are marketed."