Stickers have two layers, a printed solid shape and a protective backing paper covering the adhesive used to secure it to another object. Decals add a third layer, a paper backing that covers the decal as it is transferred by adhesion from the backing paper to another surface.
A great example of a classic sticker is the simple postage stamp, a small piece of art that has adhesive on one side and peels off a backing to be applied. Wine bottle labels, address labels and the elementary school rewarded gold star are examples of stickers.
The term “decal” comes from the word decalcomania, a process originally used to transfer designs from prepared paper onto glass or porcelain. The decal’s paper backing allows the design to be exactly placed and also keeps small pieces and parts of the decal together. Decals can be transferred by adhesives, making them technically stickers.
Water slide or slip decals are water mounted decals that are printed face up and use a glue created by water mixed with corn sugar residue from the decal paper. Temporary tattoos are reverse printed to release the ink once the paper is dampened and pressed onto the skin.