Bump pretty much means the discussion is closed. Kind of like deleting it.
Not quite …
It means a thread will be pushed back to the top of the recent threads list. Any reply would do that, but if someone is too lazy to write something (like me) I just post bump and everyone knows what it is about.
From some forum help page:
So what does 'bump' mean when people type it in a forum? In simple terms, it's used when there has been no reply to a post and as such the message has disappeared from the thread onto another page. The user replies to the post with 'bump' to get it back to the top.
It’s like a refresh … I guess deleting would be dump 
ok then this discussion is dead