i don't think he meant there was a difference, but a sukumizu generally has a distinct cut around the hips which sometimes makes it look like a too-short-to-cover-pantsu skirt (or at least that's the only way i can describe it)
A school swimsuit is a two-part swimsuit, the girls wear a small bottom thing and have a big pullover over their upper body. (you see it in some good hentai pics) They always pull it a little over their asses, that looks frickin' cute!
It's a girl, look at the other pictures under the "methylcellulose" tag...This picture truly is perfect and if a guy could pull it off...He could rule the world... I think I've caught yellow fever thanks to it.