Above the fold, as it applies to Web design, is the portion of a Web page that is visible in a browser window when the page first loads. The portion of the page that requires scrolling in order to see content is called "below the fold."
On a Web page, the point at which users have to scroll down is not constant because many variables can affect the way a page displays. The size of a device's display, for example, changes what content appears above the fold. Other variables include the end user's choice of browser, browser toolbars, browser custom setting and the operating system (OS) the device is using.
Because users engage more with the content above the fold than below the fold, key site functions and content related to business goals should appear at the top of the Web page. To understand how to work with “the fold, ” a Web designer should keep in mind the average screen sizes being used by a particular site's audience or explore responsive design techniques, an approach to Web page creation that makes use of flexible layouts, flexible images and cascading style sheet (CSS) media queries.
Above the fold was first used to describe the placement of content on a newspaper's front page. The paper's headline and lead stories are placed on the portion of the front page that remains visible to the reader when the paper is folded horizontally for display on a newsstand.
Continue reading about above the fold:
Usability expert Jacob Nielsen estimates that a webpage visitor spends 80% of the visit viewing above the fold content.
Unfolding the Fold reviews data on web page scrolling to enlighten the debate on the fold.
Search engine guru Danny Sullivan explains how Google will penalize Web pages with too many ads above the fold.