I have been waiting for someone to ask that precise question. I, too, have noted that the term "instant dry yeast" is not used for supermarket brands of yeast, and I look at every yeast section of all the supermarkets I patronize. Apparently, the term "instant dry yeast" is reserved for yeast sold only to professional bakers, usually in 1-lb. bags. However, the yeast sold in supermarkets as bread machine yeast is instant dry yeast. You will usually see it in small bottles.
The Rapid-Rise yeast is a fast-acting yeast from Fleischmann's that is for all intents and purposes an instant dry yeast. However, it is not identical to the instant dry yeast sold to professional bakers, or so I was told when I once communicated with Fleischmann's on that point (it took me several e-mails to get that admission). The Rapid-Rise yeast is intended for home consumers, usually for fast-rise applications over a period of an hour or two. My best advice is to get a 1-lb. bag of IDY, but I would use the Rapid-Rise yeast as you would IDY if you don't have another option. If the SAF "Gourmet Perfect Rise" yeast is available at your supermarket, you can use that also. It is a special breed of yeast that is intended to be used wherever active dry yeast, instant dry yeast, or bread machine yeast is called for in recipes. I have used it and it works fine.