When you promote your advertisement on 'Top Ad', you will have the opportunity to make your advertisement visible in first two slots of the advertisement page.
This will appear in yellow, having said it will increase your view by 8 times (eg: if normal ad is 1000, this would be 8000) more that your basic advertisement up to 15 day (you have the privilege to choose 3,7 or 15 days)
This is a way of refreshing the advertisement everyday, it will appear as a new advertisement everyday, usually a classified advertisements website has the highest number of views, inquiries and offers for the advertisement in the first day of posting, while that would reduce gradually..
This option 'Bump Ad' is a way to make your advertisement appear as a fresh advertisement everyday, which will increase the Number of views by 14 times that the basic advertisement (depending on the number of days you choose to promote). Bump Ad too has multiple options to promote (3,7,15 days)