git is split up in many man pages. That's generally a good thing, but you sometimes have to search or look at more than one man page to find what you are looking for.

You could try

> man -K "bare repo"

to search all man pages for that string, and you'll find that

> man git-clone

has the information you are looking for:

"--bare: Make a bare Git repository. That is, instead of creating <directory> and placing the administrative files in <directory>/.git, make the <directory> itself the $GIT_DIR. This obviously implies the -n because there is nowhere to check out the working tree."

If you have Internet connectivity, Google is also an option. Among the first hits should be the book "Pro Git", chapter "4.2 Git on the Server", which begins with a concise explanation what a bare repository is.