Thanks for the "bump" Will!
When you reply to a thread it moves the title of that thread to the top of the list for others to see. Or bump up to the top
So when most people want to keep the thread up at the top but have nothing to say they put bump. It also places this thread in your self-search list. When you do a self-search any thread that you have replied to will show up. Some use this to come back later to read a thread. Also anyone that has replied to you will show up on a self-search.