Glossaire technique
FPN - Fixed Pattern Noise
Photo Response Non Uniformity (PRNU) is - like Fixed Pattern Noise (FPN) - a way of expressing errors in the output from sensors.
Front side or back side illuminated sensors
Conventional sensors are designed to convert the light falling on the front side of the sensor to electrons. As discussed in the article Pixel size and well capacity not all the sensor surface is sensitive to light as the pixel also needs control electronics limiting the fill factor.