The word Nietzsche is using for this concept is mostly, I believe, Sitte, which means something like "customary behavior" or "folkways." One of his books talks about "the morality of mores" in this sense. Nietzsche himself, of course, didn't use the English word, and certainly had no idea of the contemporary American usage.

This is a classic problem in reading historic texts, in philosophy or any other field: You have to set aside your assumptions about what a word means, and read the text closely to see what the word means there, to that author and in that era.