Most Helpful Guy
Hourglass means you are big on top and big on the bottom with a small waist. Just like an hourglass. The triangle means you are big on top or in the hips/butt. Not both. I guess a rectangle would mean straight up and down. Never heard of that one before.
Most Helpful Girl
Hourglass - hips and shoulders are about the same width (+/- 1 inch) and the waist is at least 10 inches smaller
Inverted triangle - shoulders are visibly wider than the hips which (the hips) are only slightly larger than the waist
Rectangle - shoulders and hips are about the same width and the waist is only a little bit smaller (9 inches or less)
But at the end of the day, just dress however you want without following those bullsh*t articles about how to dress for your body type. You can see best what suits you and what doesn't.