what is a 'sticky directory'?
 

I noticed /tmp/ was a 'sticky dir' what does this mean?

Everyone can read, write, and access the directory. The "t'' indicates that only the user (and root, of course) that created a file in this directory can delete that file.

BTW: Your fav searchengine would have answered this one in a heartbeat......

Anyway: Hope this helps.

cool. how can set other this with chmod?

chmod o+t <directory> or chmod 1XXX <directory>, where XXX are the normal numeric permissions for owner, group, and other.

chmod 4777 sets suid
chmod 2777 sets sgid
chmod 1777 sets stickybit

whoops btmiller already showed the octal