Any response moves a thread to the "front of the line" and most likely into the Recent Threads section when you first log on. By "bumping", you're moving your thread to the front and increasing visibility.
The forum does have certain rules regarding bumping, but for the time being, they are only for classifieds.
The following rules are specific to “BTT”, or bumping ads to the top of the page:
1. No BTT's until your ad is 48 hours old.
2. All changes/updates should be done with the edit feature to the original post, not by adding another response.