skirtilage

Da off-limits "perimeter" surrounding a dolled-up chick dat's da diameter of da circle formed by da lower hem of her dress.

Once a hot number sits down, da radius of her skirtilage gets shortened considerably; in fact, if da lower half of da gown's fabric presses against said attractive gal's knees, dat might "conceivably" allow you to actually lift up said interfering material and perform da delightful "conceiving" action dat you'd been wanting to.