Well, not to duck the question, but does it really matter? OK, maybe if you're entering a contest for "large format" practitioners, then you'd want a definition. Otherwise, it's really a matter of semantics. What we now call medium format used to be called "miniature" many decades ago. But, my two cents...Polaroid 665 gave negatives that are 3 1/4 inches by 4 1/4 inches. That's considerably more than what is "normally" considered medium format these days (2 1/4 by 2 1/4, 2 1/4 by 3 1/4) -- probably about 180% of the latter. So you'd be justified, I think, in calling it large format if you wish. Plus you have to file the negs individually as do large format users --it's not roll film.