These are creases in a dress or skirt caused by panties. Usually panty lines show up when a dress is too tight or too thin and appear as lines around the waist or across the cheeks. Panty lines are generally considered unattractive. I don't know why. It's not like it's a big secret when a woman is wearing underwear is it? Anyhow, a woman's two basic solutions to the "problem" of panty lines are: a) wearing heavier clothes like a flannel granny dress or, b) wearing less underwear like a g-string (or maybe even going commando (pantyless).)