A Die Cut sticker is one where the blades have cut through the vinyl as well as the paper backing. The end result is a sticker with backing that’s the same shape as the sticker itself.
So, for example, if your sticker is shaped like a cloud, the final product, backing included, will be shaped like a cloud.
A Kiss Cut sticker is one where the blades don’t go as deep and only cut the vinyl, leaving the backing intact. In this case, the final product is usually a rectangle or square of backing and vinyl, but when you remove the sticker itself from the backing, it’s been cut around the design’s shape.
For example, when it’s still on the backing, the sticker is rectangular or square, but when you remove the sticker, it’s the shape of a cloud.