In the print packaging industry, a dieline is a template that ensures the final physical package has a correct layout. This template is a diagram or model that shows all the cut lines and folds of a package in flattened form.
Dielines are created by die cutters, printers, or graphic designers to help produce various types of packaging, such as boxes, folders, envelopes, etc. They consist of three lines: the cut, perforation, and fold lines.
Once the design goes to the printer, the dielines indicate where the machine should make the cut and perforation, readying the package for folding.