lol that´s actually becoming a common question!
it´s when a Scort blows away a puny civic in a race and the civic driver´s jaw drops to the floor, it goes ´bump´. ;-)
but in another case, when no one replies to a thread in a long time, and it leaves the "Last 25 Posts", and the original poster still wants feedback they reply to their own post, bumping it back to the top of the list. hence, ´bump´