Honestly this is a good question. I don’t know if there’s been any work done on defining this, but I think it’d be interesting to run some studies to see what the consensus within the population is, if there is one. Personally, when I imagine a cure I think of something that renders it possible to not stutter without continuing treatment; in other words, after you do this thing, you don’t need to maintain it with pills, therapy, nothing. This is also probably the least realistic way to treat the word in this context — if we figure out that stimulating a certain brain region “cures” reduces stuttering to zero for six months, after which it would have to be repeated, that would still be a humongous win for the community, I think.