Bump is usually used by the Mods to bring a thread back to the top that may have gotten lost in the shuffle and perhaps a member has asked a question that is covered in a thread. When we bump threads sequentially we usually remove the previous "bump" posts to save space.
Another way to show a new member where a thread is would be to post the link if you do not want the whole thread pulled back up.
Thats it, no mystery. Thanks all for your help and know I appreciate it very much.