For many years, what a restaurant would call London Broil was the butcher's term for flank steak. Now London Broil is a tough piece of meat that if it is flank steak it is tough enough. It if is being sold as London Broil, but the meat is (primally) top round, it's even tougher. According to Wikipedia:
Although American butchers may label a cut of meat "London broil", the term does not refer to a specific cut of meat but to a method of preparation and cookery. The cut of meat traditionally used is flank steak, but butchers may label top round steak or roast as London broil.
What was 99¢ a pound for a long time was retailed as London Broil. As it had no long fibers, it was meat from the Round. I disagree with the Wiki entry somewhat. It's not a means of preparation. London Broil, by name, is still retailed here in America's second largest city. I can only guess that the markets want customers to think they are getting flank steak (now an expensive cut of beef), when the customer is getting an inferior cut, compared to the flank steak.
The Standing Prime Rib Roast
Almost everyone I know likes a Prime Rib Roast. Definitions do not differ so much about this cut of beef. Here is as definitive a characterization as I can give. As I have ever found.
The Complete Book of Outdoor Cookery
by Helen Evans Brown and James Beard
Garden City : Doubleday, 1955
“Chapter 7 -- Roasts
Standing Rib Roast
In America, the favorite roast of beef is a standing rib one, consisting of from 3 to 5 ribs (though all 9 may be used for a large party), with the bones left on. The first 4 or 5 ribs are sometimes called prime ribs, and are preferred. [for their tenderness - Je suis flâneur]. Connoisseurs esteem the standing rib roast because of the extra flavor the bones impart to the meat.”
So it is possible that the Standing Prime Rib could be called the Standing Prime Rib if it has all 9 ribs or even if it has but 4 to 5 ribs. The restaurant is swanky if using only the first 4 and not-as-swanky if using the whole rib section.
2 rib roast - 4 to 5 pounds
3 ditto 7 to 8.5 pounds
4 ditto 9 to 10.5 pounds
5 ditto 11 to 13.5 pounds
6 ditto 14 to 16 pounds
7 ditto 16 to 18.5 pounds
The foregoing being a bone-in roast. Ideally you will have a spit-jack to turn the meat (otherwise called a rotisserie) and a catch basin to save the drippings.