the section of a Web page that is visible without scrolling.
The fold varies depending on the resolution settings on a visitor’s monitor. At lower settings the fold is relatively high on the page. At higher settings the fold extends much further down the page. Decisions concerning what goes above or below the fold are often made based on a minimum targeted resolution.
Advertisers often look favorably at placements that are high on the page, assuming that their ads will be viewed and clicked more often. Some banner exchanges are even more direct, only swapping above-the-fold impressions for other above-the-fold impressions.
If a banner ad is placed above the structure containing the main content, then the ad can be viewed before the main content loads. When a banner is allowed to pre-load, being above the fold may be favorable in terms of generating awareness.
However, if a banner ad is being served from an overworked ad server, the image may not render before the visitor scrolls down the page. In this case being above the fold may be unfavorable.
above the scroll
Banner Ad Placement Study