Above The Fold refers to the part of the screen where a user does not have to scroll to see content. It is a reference to newspapers where the top part of the page is above the fold..
The content that a user sees upon opening a document without having to scroll. All content below this is considered below the fold. Good web designs contain the most important info above the fold.
Originally, this term referred to newspapers - the top half of the page that could be viewed when the newspaper was folded. With reference to web pages, the term refers to the section of the page that can be viewed without scrolling down.