The most fundamental question about pixels

I have a question, which might be funny to some of you …

A pixel on the screen … is it a hardware-wise component :look: … in other words, does its size on the screen remain the same no matter what happens?

Or does it change according to the configured resolution? I feel that I am very confused!!
I always thought that a pixel has certain dimenions and never changes ,…

I dont even know what I wanted to ask anymore. All I want is someone to hit me on my head. :egg: