Q: What do the markings "sell by," "use by" and "best by" mean? When did these markings appear? I don't recall seeing them before about 10 years ago. There might have been dates on the package before, but you might not have been able to understand them. It used to be common for companies that handle perishable food to mark the packages with codes so that the guy who drove the egg truck or the bread truck knew how long something had been on the shelf.

These days, you see more actual dates. It's called "Open Dating" when a package has a date instead of a code. But the language still gets confusing.

Except for certain products, including infant formula and some baby food, product dating isn't required by federal law, and there isn't a universal system. Making it even more confusing: Some states require certain foods to be dated, and others don't.

However, when you see open dating on a perishable product, it usually works this way:

Sell-By is used by the store or the food company representative to show when to take something off the shelf.

Best-By (or Best If Used Before) is a quality recommendation. It has nothing to do with safety. The product may be fine for a least a little longer.

Use-By is the latest date recommended for peak quality, although the product may be OK for a day or so longer.

Charlotte Observer Food Editor Kathleen Purvis answers cooking questions. Send queries to kpurvis@charlotteobserver.com