In UNIX, the name of a file or a directory is called a link, and it is possible for a file to have more than one name (in the same or another directory), provided that they are on the same filesystem (or within the same btrfs subvolume). This is called hard-linking.
In GNU/Linux concretely, directories can no longer have user-created hard-links, but every directory on the system contains two system-created hard-links, i.e. one to itself (.) and one to its parent directory (..). These are necessary for being able to search and/or navigate the directory. See my tutorial below… 
Given that these two names — “.” and “..” — start with a period, they are hidden by default.
[nx-74205:/dev/pts/3][/home/aragorn]
[aragorn] > cd Downloads
[nx-74205:/dev/pts/3][/home/aragorn/Downloads]
[aragorn] > ls -l
total 0
[nx-74205:/dev/pts/3][/home/aragorn/Downloads]
[aragorn] > ls -la
total 0
drwx------ 1 aragorn aragorn 0 Sep 4 06:40 .
drwx------ 1 aragorn aragorn 1096 Sep 8 03:00 ..
[nx-74205:/dev/pts/3][/home/aragorn/Downloads]
[aragorn] >