Anonymous wrote:It is meant to bring the post back up to the top of the list of threads to try to get someone to respond.
From wikipedia: "When a member posts in a thread for no reason but to have it go to the top, it is referred to as a bump or bumping. It has been suggested that "bump" is an acronym of "bring up my post";[15] however, this is almost certainly a backronym and the usage is entirely consistent with the verb "bump" which means "to knock to a new position"