What is the purpose of the design specification for both the designer and the manufacturer?

A design specification is a set of design criteria that is created before the designing process begins and it is used to set targets and parameters for the designer in order to ensure their product is relevant for what it is being designed for. For the designer, the purpose of the specification is to set out the specific parameters - this could include the product function, aesthetic qualities and the target market, as it ensures that while designing, the designer has criteria to evaluate their designs against to see where improvements could be made. For the manufacturer, the purpose of the design specification can involve criteria such as material selection and manufacturing processes/methods or finishes, in order to ensure that the product is manufactured to the quality that is required and in the correct way as per the design.