Reg wrote:

>> It is only prime rib if the meat is graded "prime"..otherwise it is a
>> standing rib roast.
>
> "Prime Rib" refers to a cut, not a grade. They only coincidentally
> share the word "prime". This is a long standing source of confusion.
>
> You'll find texts going back as far as 18th century England, or even
> further, that mention prime rib. The term predates the USDA and USDA
> grading by at least a century.
>
> Plus, don't forget about all the other English speaking countries. It's
> safe to say the USDA does not grade all their prime rib.
>

According to Barron's Food Lover's Companion (1990)-
"The term "prime rib" is often incorrectly used as a label for what is
actually a Rib Roast. Culinarily, the term "prime" actually refers to
the highest USDA beef grade. It's only given to the finest beef,
hallmarked by even marbling and a creamy layer of fat. Very little prime
beef makes it past the better hotels and restaurants or prestige
butchers. The best grade of beef generally found in supermarkets is USDA
Choice. Therefore, although "prime rib"is how rib roast is often
labeled, chances are that it's USDA Choice beef."