What is the difference between Prime Rib and a Standing Rib Roast?

I just happened across this older question and found the answers provided, including the information in the link to wikipedia to be incorrect.

All Prime Ribs are Standing Rib Roasts, not all Standing Rib Roasts are Prime Rib.

• [see edit below] A "Prime Rib" is a standing rib roast, from a beef that has achieved a USDA Grade of "Prime".
• Bone-In or Bone-out are separate distinctions the can be applied to any standing rib roast, regardless of grade.

U.S. Prime – This is the highest grade of beef with the most fat marbling. This meat is very tender and only accounts for about 2.9% of all graded beef. U.S. Prime is usually reserved for high end dining establishments. Because this beef has such a high level of fat marbling, it is excellent for dry heat cooking methods. from: http://foodreference.about.com/od/Meat/a/Usda-Beef-Grades.htm

Also, technically a Prime Rib is not a 'steak' but rather a 'slice of roast'. If one takes a slice from a raw rib primal and grills or broils it as a steak it is a "Rib Eye", and can also be either "bone-in" or "bone-out". (the use of the word 'primal' refers to a primary cut of beef, the first cuts a butcher will use to section a beef beyond quartering, it is utterly unrelated to the word "prime" in "Prime Rib" )

[Edit 12-21-17: Additional research indicates I had causality inverted. The USDA choose the term "Prime" because of the popularity of "Prime Rib", a term that apparently existed before the USDA grading system. More importantly the 'Prime Rib' is cut from between the #6 and #12 ribs, but may be of a grade other than 'Prime'. However, the initial point remains true that "All Prime Ribs are standing Rib Roasts, but not all Standing Rib Roasts are Prime Ribs". The 'Standing Rib Roast' may include (or be exclusively) from outside the 6-12 range. The potential difference being from where within the rib primal the roast is cut.]

Prime rib can be either a steak sliced from the roast or the entire roast. In other words, it isn't a precise term.

The standing rib roast is more precise. You can get more than one prime rib steak from the standing rib roast. The standing rib roast must have come from at least 2 of the ribs.

A rib eye roast is a standing rib roast with the ribs removed.

The prime rib (standing rib roast or steak cut from that area) is actually not required to be USDA prime beef.

The primal is called the 7 bone rib, the 4 long bones from the loin end are called the prime rib, typically used for bone in steaks and ribeye steaks because the muscle, along with the bone is longer. The 3 shorter bone section from the chuck end is the standing rib, more suited for premium oven roasts as it is more heavily marbled. That said the meat is equally tender throughout with heavier pockets of fat developing towards the standing rib section, so the whole seven bone section can be cut for either steaks or roasts with fat content being the only difference.

Rib roast is a cut of beef including bones (unless it is boneless or Eye of Rib).

Prime is a grade of beef, with high amounts of marbling and fat so as to achieve optimal tenderness and flavor.

The description "Prime Rib" was in use before the FDA started using "Prime" as a grade of beef, therefore some roasts called "Prime Rib" might be from non-Prime-graded beef.

You can get a rib roast in any grade or breed of beef (grade descriptions from USDA.gov, specifically: [https://www.fsis.usda.gov/wps/portal/fsis/topics/food-safety-education/get-answers/food-safety-fact-sheets/production-and-inspection/inspection-and-grading-of-meat-and-poultry-what-are-the-differences_/inspection-and-grading-differences/!ut/p/a1/jZFRT4MwEMc_DY9di8yF-UZIzIYOXBYd42Xp4FpIoCVtkcxPb8EHnRm69qV39_tf2__hDKc4E_S94tRUUtB6iLPFkWzJwl2GJEqW7iNZx2_b5CkMib-7t8DhDyD2btRPrID8p49uuOBObcINx1lLTYkqwSROORhEhe5BaZwyKQukKQNzRozmBukSwNhCq2TR5YMVFi6sVLcwhjj9Po8lrmhRCY4kQw1QM-Za2dVGnVFfDgkFyJSAiooxUCBy0MfJLj8gvMfZ5ReJa_c69nbzVRR7JJn_Bq7M4AuYNtm6yGt5Ggd-CMTJ861dCoZHqFmnbLo0ptUPDnFI3_czLiWvYZbLxiHXJKXUBqeXJG6b1_TjOViR6qXZ-zr4BEpuht4!/#5)][1]

Prime: "is produced from young, well-fed beef cattle. It has abundant marbling and is generally sold in restaurants and hotels. Prime roasts and steaks are excellent for dry-heat cooking (broiling, roasting, or grilling)."

Choice "is high quality, but has less marbling than Prime. Choice roasts and steaks from the loin and rib will be very tender, juicy, and flavorful and are, like Prime, suited to dry-heat cooking. Many of the less tender cuts, such as those from the rump, round, and blade chuck, can also be cooked with dry heat if not overcooked. Such cuts will be most tender if "braised" — roasted, or simmered with a small amount of liquid in a tightly covered pan."

Select "is very uniform in quality and normally leaner than the higher grades. It is fairly tender, but, because it has less marbling, it may lack some of the juiciness and flavor of the higher grades. Only the tender cuts (loin, rib, sirloin) should be cooked with dry heat. Other cuts should be marinated before cooking or braised to obtain maximum tenderness and flavor."

Standard and Commercial "frequently sold as ungraded or as "store brand" meat."

Utility, Cutter, and Canner "seldom, if ever, sold at retail but are used instead to make ground beef and processed products."

Certified Angus Brand "Choice or Prime graded beef from black-hided cattle (typical of the Angus breed), evaluated for marbling, size and uniformity. " (https://www.certifiedangusbeef.com/cuts/grades.aspx)

My recent comparison of Standing Rib Roasts at a large grocery showed that the Prime graded beef had thick marbling and large pockets or globs of fat; the roasts labeled Angus had very fine threads of marbling throughout, and the Choice had no marbling at all. I got Choice, and though the rare was acceptably flavorful and tender, it was by no means comparable to the juicy tender Prime and Angus I've gotten previously.