Git: Where exactly is the “working directory”?

I am going through some Git tutorials. The concept of a “working directory” keeps being mentioned, however, none of the tutorials or documents I read points out where or what this “working directory” is.

I have thought that it was actually the .git‘s parent directory, a.k.a the directory I run git init in. But the video tutorial I am watching talks about the state of nothing to commit and “working directory clean“:

In fact you can actually make a copy of the repository, and make that copy so that it does not have a working directory, this is actually called the bare clone. This is actually what GitHub uses.

If my understanding of the “working directory” is correct, how can a repository not have a “working directory“? And what does it mean, when it says that GitHub uses a “bare clone“?