Most relevant excerpt (MRE): "You can still see dead stuff if you set showdead to yes."
The rest of the comment for context: Your comment is still alive
http://news.ycombinator.com/item?id=27969
even though the post you commented on was deleted.
I just added deletion. When something is deleted, it really goes away. This is different from marking something as dead. You can still see dead stuff if you set showdead to yes.
Deletion is for submitters who change their mind; marking stuff as dead is for editors to do to spams and offtopic submissions.