Other forms: creases; creased; creasing
A crease is a fold, wrinkle, or line, like the crease in your perfectly ironed pants or the worried crease in your dad's forehead when he sees you heading out into the snow without a hat and scarf.
A crease can be straight and sharp — think of the creases in a folded paper airplane — or something more like a soft indentation, like the crease in your blankets telling you your cat was just there. It's a verb too: "If you lie on the floor, you'll crease your ball gown!" Etymologists guess that crease comes from crest and its root, which means "to turn or bend."