@ShinkuKaru in the ancient forums days, posts would bump up to the top of a forum whenever a new message was posted, there wasn't much "sort by" functionality. So if you had a suggestion for a game, or were trying to trade an item, you would post "bump" to bring your post back up to the top. Unlike stuff like reddit where conversations die after a few days as the post dies, forums enabled you to revive posts.
This became known as bumping