By default, rm -r will not remove non-empty directories. However rm accepts several options that will allow you to remove any directory. The rm -rf statement is famous because it will erase anything (providing that you have the permissions to do so). When you are logged on as root, be very careful with rm -rf (the f means force and the r means recursive) since being root implies that permissions don’t apply to you. You can literally erase your entire file system by accident. [feedback]
paul@debian7:~$ mkdir test paul@debian7:~$ rm test rm: cannot remove `test': Is a directory paul@debian7:~$ rm -rf test paul@debian7:~$ ls test ls: cannot access test: No such file or directory paul@debian7:~$