N for Noise Reduction
With improved sensors, came noise too. What is noise, in terms of photography, if you are curious, head over here.
Noise reduction is inbuilt in the camera bodies generally, and also applied during developing the final image. It takes care of the grains at a compromise with the sharpness. The changes are generally subtle and the results are actually better. I find, keeping sharpness and noise reduction sum up to 100 or max of 150 makes my low lights photos fine. I recommend, try out the different settings and softwares too. Trust me, you ll need this someday.