What does "Updating Shaders" mean?

I posted several questions about this problem with “Updating Shaders” taking a very long time.
Is this normal?

What does it mean?

I never got an answer, I’ve googled around, and other people who asked this question… funny enough, never got an answer.

Please explain to us, what does the “Updating Shaders” mean, and how can it be reduced in render time, because it really eats up 80 % of the entire render time for every frame.

This problem needs to be addressed. I need an answer!