What is this bump?

[sirensis]

Hello!
I have seen a snake with i weird bump on ist back and i heard it was a kink.
I have never heard the term kink before and never seen one until now so i´m wondering if someone can explain to me what a kink is...
When i first saw it i thought it was broken but apparently it a kink so what the heck is it??

I have heard from so many different people so many different things about kinks and i have no idea what is right and what is wrong.
Some say they are harmless and some say they are painful for the snake.
They can live a full and normal life/they will die or will have to be put out.

The snake i´m talking about is moving without problem exept for just were this kink is.
It can bend perfectly to the left but not the other side.
The rest of the snake can bend normally.