DFM, or designed for manufacture is the process by which your product is designed with successful commercial manufacture specifically in mind. Typically it will focus on minimising the complexity of parts and manufacturing operations. This is usually done during the design or early product development phase, where it is easier and cheaper to make changes, to reduce manufacturing costs later on.
At Tharsus DFM is a core part of how we work as a business, when going through new product development, we want to make sure our customer's product is fit for manufacture.