yup, Knitting Nacy I have heard, too. But the abundance of names leads me to the conclusion that it is just "that knitting thing" for most
I made those cords, too. I braided them for a dog leash, I sewed them to flat round pieces for coasters and pot cosies, I made not much more with them.
I have seen great items done with it at our yarn shop lately:
you crochet a mesh ( a tripple stitch, 5 loop stitches... and so on, next row offset to the middle of that grid). You make a pullover, vest, handbag... that way.
Then you make that endless I-cord and weave it in all neat. The result is a fabric with a lot of structure and interesting play on technique.
They ususally use a self striping yarn for the I-cord. But you can also use that for the crochet. Or just use different colors.
I would also think you could make that bag in felting and then weave to get even more of a structure difference.
And then there is that pullover in Power Cables that I really like and that weaves that cord.
I also would use it for pullstrings in garment, like bottom or waistline of a pullover, hood of a jaket and so on. Also for wrap jackets to close them off.... all that.
So: I do not use I-cord in long pieces all that often but I might. And then I know how to knit it, I guess.