chmod 00000 makes the directory/file inaccesable to owner and group. The only thing you and the group that owns the file can do is remove it with rm -rf tmp/. Nothing better than an example:

$ mkdir tmp

$ chmod 00000 tmp

$ cd tmp

bash: cd: tmp: Permission denied

You can see the directory with ls -l

d--------- 2 rinzwind rinzwind   4096 Oct 13 14:35 tmp

and but only with sudo permissions can you enter the directory ...

 $ sudo su

 # cd tmp

 #

Regarding the other posts: yes you can remove a file/dir that is chmodded to 00000:

$ mkdir tmp

$ chmod 00000 tmp

$ rm -rf tmp/

$ touch 1

$ chmod 00000 1

$ rm 1

rm: remove write-protected regular empty file `1'? y

$ 

As the owner you are also allowed to reset the permissions. That is something someone else (except for root) is allowed too.