When you use rmdir without the -r option, and the directory is not empty, you will get this message

rmdir: failed to remove `tmp': Directory not emptyill get a 

So if you want to delete a directory with all its contents, you may use two different commands.

rmdir -r directory

or

rm -rf directory

Use this with care, as its results can not be undone, and better if you never use it as root.