What are these designations on a sensor datasheet?
Image sensors are sensitive to photons, and at the most basic level, each "pixel" effectively counts the number of photons that they sense. That's the DN or digital number, which are more important when you're working with raw data. (Before processing, filtering, etc.)

RMS is root mean square, common terminology for averaging a continuously changing value.

PRNU is photo-response non-uniformity. It's a way of characterizing the performance of individual sensors across the CMOS image sensor.

FS just means full-scale.

LE is linearity error. From the EMVA Standard for Characterization of Image Sensors and Cameras:


  The linearity error is then defined as the mean of the difference of the maximal deviation to the minimal deviation
  $$
LE = \frac{max(\delta_y)-min(\delta_y)}{2}
$$
  and thus defines the mean of the positive and negative deviation from the linear regression.


I'm not sure what you mean by threshold sensitivity. Do you mean the minimum threshold at which it detects light? That seems to be given in the 6V/lux-s (volts per lux-second) sensitivity property. However, you'll have to work from there; I'm not an expert in image sensors (sorry!).