Question: what is gray gamma 2.2?
Answer: Gray Gamma 2.2 comes with PhotoShop. Now, there are two reasons that one uses a profile such as gray-lab or Gray Gamma 2.2 for B&W work instead of sRGB. sRGB is slightly "broken", there is a small discontinuity in its tone curve (the curve that maps "lightness") which occasionally results in visible banding in images.