This means posting something in your thread to try to increase its profile and exposure to other members, without adding anything of real substance to your thread. Your post will be removed and the thread closed (to prevent further bumping), you will also be warned. Please note that repeat incidences of bumping can result in a vacation for you.
The only time you can post in your thread is to reply to other comments, or to post a significant change in your offer. Anything other than this will be considered bumping.