The short size has to do with the actual inseam of the pant. For example, the Missy pant length has a 31 inch inseam and the short inseam has a 29” inseam. With these sizes, additional adjustments aren't made anywhere else on the pant. The petite on the other hand, has a shorter rise and inseam. So the rise of the pant will fit in proportion to the body. So, if you have shorter legs but a longer torso, go with the short inseam. If you have a shorter torso and legs, go with the petite. I hope this helps!