+0
The doors of the bus were jammed and the windows had to be broken to rescue the people.

I could understand the highlighed parts as, "The doors of the bus were unable to move". Am I right?

If I'm correct, I wonder why it could not be moved. Are the doors were locked?
+0
I've not heard the word 'nibbed'.

It means they were stuck and couldn't be openend. It sounds as though the bus has been in an accident - possibly the doors were damaged and no longer work? Otherwise they simply weren't working properly and were stuck in the shut position, which is why the windows had to be broken. Jammed doesn't mean locked.
Comments  
User_gary
The doors of the bus were jammed and the windows had to be broken to rescue the people.

I could understand the highlighed parts as, "The doors of the bus were unable to move". Am I right?

If I'm correct, I wonder why it could not be moved. Are the doors were locked?

Hi! "The doors of the bus were nibbed". It's another interpretation of the word "jammed". Therefore there is no another way to leave the bus.
 nona the brit's reply was promoted to an answer.