what does prompt [master +1 ~0 -0 !]> mean when using git command line

what does prompt [master +1 ~0 -0 !]> mean when using git command line

I am a newbie of git, and I am learning it right now. Just do some
practice by using the command line with one of my repositories on github.
After a few git commands, I find my command line prompt change from
[master]> to [master +1 ~0 -0 !]> What does this mean?
By the way, Git for beginners: The definitive practical guide is really a
good "beginner's practical guide to Git".