Technically there is no such thing as a "Prime Rib Roast"
Prime is a designation of the quality of the beef, it is the highest quality and contains the most internal fat or "marbeling", consequently it is the best tasting and tenderest meat.
And of course the most expensive.
Most USDA Prime beef is sold to high end restaurants. USDA Choice is the best that most of us can get out hands on, including most restaurants which feature "Prime Rib" on their menus. USDA Select is the next grade down and the less expensive grocery stores will mostly be selling Select beef at far better prices. But you get what you pay for and this really isn't very good beef.
The lowest grade is USDA Standard. This is the meat your gonna find in a McDonalds burger, canned beef soups and stews, processed and frozen prepared foods, cheap premade frozen hamburger patties. It's truly awful beef but can be made palatable with sufficient processing, tenderizing, pressure cooking and god knows what all they do and add to it to get you that cheap frozen lasagna and teevee dinners..
