A decal is a specific type of sticker. While a sticker is a more generic term that can refer to anything from novelty adhesives, labels, stamps, etc., a decal is an adhesive design that can be transferred from one surface to another. A sticker usually has two layers — a decorative layer with an adhesive backing supporting a design on the front and a layer of paper on the back that is peeled off to apply the sticker. On the other hand, decals mostly have three layers — a layer of paper on the back and one on the front with the decal in between.