Collaboration between a customer and a supplier to design both a component and its manufacturing process. 

Usually the customer provides the cost and performance targets and the supplier takes care of the detailed design of the component and the manufacturing process (equipment, layout, quality etcetera). The supplier often stations an engineer at the customer's site to ensure that the component is properly matched to the final product, thus keeping the overall cost as low as possible. 

Design-in is the opposite of work-to-print; here, the supplier is simply given a complete design to develop and produce.