A die is a tool used in the manufacturing of parts by the molding, forging, swaging or stamping processes. They are typically manufactured by mold or tool makers. It is also often used with a movable part called a tool, and both are often created by a specialized machinist craftsperson called a "Tool and Die Maker". The term die is also applied to a device for cutting male threads and a part of a device for creating wire.

A die in manufacturing is a metal block that is used for forming materials like sheet plastic and sheet metal. For the vacuum forming of plastic sheet only a single form is used.