'What does an exclamation mark (!) before a statement do? [duplicate]

I was trying to install the dark theme in Jupyter notebook by typing this in notebook

pip install jupyterthemes
jt -t chesterish

The first command worked but I got some error in the 2nd one. Then I wrote this

!jt -t chesterish

And it worked. What did the exclamation mark do?

P.S. I am extremely new to python, just started last week

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