1. Overprint: print one color on the surface of another color, ink will be mixed together.
2. Register: In order to prevent each ink layer from mixing, the above layer will hollow out the below one, perfect or exact register also called Kiss Fit.
3. Trapping: To avoid the potential problem of misregistration, and the resulting gaps between colors that are designed, In general, trapping is the overlapping of colors to prevent misregistration and the resulting gaps of paper showing through, commonly spread the lighter color and the underneath color.