What Do the Experts Say? Linux (GNU coreutils 8.5)

• man rm (excerpts slightly re-arranged):

        rm removes each specified file.  By default, rm does not remove
        directories.  Use the --recursive (-r or -R) option to remove each listed
        directory, too, along with all of its contents.

       -r, -R, --recursive
              remove directories and their contents recursively

       -d, --dir
              remove empty directories

       -f, --force
              ignore nonexistent files and arguments, never prompt