what fork means in github code example

Example: test project at a previous point in history in github

$git checkout 9193513c5b1bc063b35b830101fe7cf0d9ecffca 
   Note: checking out '9193513c5b1bc063b35b830101fe7cf0d9ecffca'.
    
   You are in 'detached HEAD' state. You can look around, make experimental
   changes and commit them, and you can discard any commits you make in this
   state without impacting any branches by performing another checkout.