A die cut is an image made by a die cutter. There are manual die cutters (Cuttlebug, Big Shot, Side kick, Creatopia, Grand Calibur) and there are electric die cutters (Cricut, Gazelle, Pazzle, Black Cat Cougar, Vegabond, E-Craft, slice). The machines cut out various shapes from cartridges, die plate, computer or sd card base.
The manual die cuts cannot be manipulated. On the electronic systems you can make the images smaller or larger. On some systems you can weld images and manipulate them to make new images (if you have the component to do so). HTH