What is the difference between Prime Rib and a Standing Rib Roast? (and a "rib eye roast" while you're at it)
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.
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.
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" )