'checkout' in english language means an act of leaving. git checkout refers to the action of swaping between different repository branches/files/commits.

It helps in switching between different branches that have been created by git branch. It can be understood as the method of selecting the current line of development one has to work on. It helps in updating the files in the current directory to agree with the version of the file in the branch

git checkout is different from git clone in the way that checkout switched between the branches of code already on the local system while git clone works to get code from remote repository.