DFSS (Design for Six Sigma) is used to design a new process, product or service, or to redesign an existing process, product or service from scratch. This contrasts with the normal Six Sigma approach that is used to improve existing processes, products or services.
For example if you wanted to replace a manual accounting system with a computer-based one then you might use DFSS.
Design For Six Sigma uses the DMADV or DMADOV sequence rather than the DMAIC sequence.
Methods used in Design for Six Sigma include Porters Five Forces Analysis, Pugh Analysis, TRIZ and the Taguchi Approach to the Design of Experiments.