Delete / Remove a Directory Linux Command

How do I delete or remove a directory?

Use the rmdir command. This command remove the DIRECTORY(ies), if they are empty. Open a command-line terminal (select Applications > Accessories > Terminal), and then type the following command to remove a directory called /tmp/docs:

 
rmdir /tmp/docs
 

If a directory is not empty you will get an error:
$ rmdir letters
Output:

rmdir: letters: Directory not empty

You can cd to the directory to find out files:
$ cd letters
$ ls

Linux Remove Entire Directory Command

To remove all directories and subdirectories use rm command. For example remove letters and all subdirectories and files inside this directory, type the following command (warning all files including subdirectories will be deleted permanently):
$ rm -rf letters/

Resource: nixCraft