Why Using the kcl means potassium chlorideinuv vis calibration

Are you asking why is KCl used in UV/Vis calibration? I'm afraid I don't understand your question at all so let me take a guess at what you are asking.

Stray light" is light from wavelengths other than the desired wavelength.

A solution of (typically) 1.2% KCl is commonly used for stray light corrections in UV/Vis spectroscopy. The KCl provides ionic strength to the solution (hence, it changes the refractive index so as to be similar to comparable solutions), but it doesn't absorb in the UV or Visible region (except above its cut off wavelength). Therefore, light hitting the detector will be all stray light if you're selecting a wavelength where KCl does not absorb. KCl cuts off at 200 nM.

I was curious about something similar... Does that mean it is basically a filter? Like in electronics, a low pass filter?

What you're doing with the KCl is getting a reading of the stray radiation. You subtract that reading (it's a single number) from the single absorbance number you read when a sample is in the light path. Stray radiation causes readings to be too high. KCl is in there only to approximate the matrix that the sample would be in.

This is a correction. It is not a filter of any kind. It doesn't have anything, that I can think of, in common with a low pass filter.