What role does git subtree play here?

Question

git

I found instructions on how to upload projects on gh-pages
https://habr.com/ru/post/262095/

in the 4th paragraph there are the following lines:

4) Deploy subtree to the gh-pages branch (we are now in the master branch)
git subtree push --prefix dist origin gh-pages

But what exactly does the git subtree push --prefix dist origin gh-pages command do, and what is it for?
What does "Deploy" mean, why exactly do we do it?

Answer 1

Roughly, but essentially: the command pushes the dist directory (compiled code) to the gh-pages branch (what will be displayed in the github pages of the repository).