You could search the internet and find definitions for six sigma, lean design, and black belt, and then you would learn that each business might apply them differently.
You might also learn that these three terms can be used across many types of projects, so when looking at their meaning at CES, we refer to the product design process (big picture), not just the production of one single part (small detail).
The product design process includes the 5 design phases from CES, and it also shows the other logical steps so you think about them in advance. Think of it as looking down the road when you are driving; you can see the signs like stop, yield, turn etc, but if you don’t look forward you will likely have an accident.
Without getting into too much detail, six sigma is the application of common sense, and by looking down the road at known and predicted part and process tolerance we can design your product so it has the widest process window. Since we are watching the signs, you get a product that works every time.