Every directory on a Unix system (and probably every other system too) contains at least two directory entries. These are . (current directory) and .. (parent directory). In the case of the root directory, these point to the same place, but with any other directory, they are different. You can see this for yourself using the stat, pwd and cd commands (on Linux): $ cd / $ stat . .. bin sbin ...
directory - What are ./ and ../ directories? - Unix & Linux Stack Exchange