I'd have thought the difference would be whether it's a domain that you're speculating might be valuable to anybody, versus one that you assume to have value to

I'd have thought the difference would be whether it's a domain that you're speculating might be valuable to anybody, versus one that you assume to have value to someone specific. E.g. buying "learn-brainfuck.com" because you think it's going to be the next big language, vs. buying "github.kr" for when they eventually open a Korean office. Not that one's any better than the other, but I think people tend to call the former "speculation" and the latter "squatting".