Cut-out
From wipipedia.org
File:Doubleslitskirt.jpg
300px
A cut-out is a large hole deliberately cut in a piece of clothing to reveal the wearer's bare flesh underneath. The commonest place for a cut-out is over the breasts to emphasise cleavage.
Slit skirt
A similar idea is to have a long slit in a dress or skirt from the hem upwards, so that even though the skirt is not short, the thigh may be glimpsed as the wearer moves. Depending on the length of the slit and what else is being worn, it may be possible to view a stocking top or even panties (unless the wearer is going commando).
