What is the pinned symbol button?

[RESTRICTED ACCOUNT]

Hi there.
I was wondering about the role of this symbol in the dialog title bar. (´・ω・｀)What's this？
The 4th one.


I pressed this button in order not to accidentally close the dialog I care about. Yeah, I expected such a feature from this pinned symbol.
However, there was no such function. Pinned dialogs can be easily killed.
Then I came up with the possibility that relocation of it would be prohibited. Unfortunately my next prediction didn't hit either.
So I ask a question. What does this button do?

Anyway I wanted a button to keep the dialog from closing. Is it ideal to have a symbol like a padlock?

[Mariculous]

Pinned windows are not closed when using the backspace key, which is "close all, except pinned"

[RESTRICTED ACCOUNT]

Thank you for the explanation. I didn't notice it. I used Esc only because I always used the keyboard with my left hand and the mouse with my right hand. (´・ω・｀)

[Mariculous]

I used Esc only because I always used the keyboard with my left hand and the mouse with my right hand

Everybody does that I guess.
Trust me, it is really possible to access the whole keyboard with only the left hand