When one posts a question and nobody replies by time the post gets to the bottom of the newer posts list, so the OP (original Poster) bumps the post (makes it to the top of the new posts) by posting nothing relevant just saying: bump. It increases the visibility of the post, thus better chances for somebody willing to give an answer.
Oh I see, Well what if someone else addresses your post with the term BUMP? It's not an insult then. thanx for the info