More accurately seen from the perspective of the layout designer and the desires of the content editor, "the fold" is actually the point where the content itself is divided by a re-configuration of the container (newspaper/magazine/brochure) by the reader. In print, the reader modifies the form of the instrument by physical folding; in the case of online/digital the fold of content occurs more as a result of window size/zoom preferences of the user. Calling the point where your content is sliced -in half or otherwise- a "fold" works in that context; but it cannot be argued that there aren't more appropriate phrases for the term. Its just that this publishing business is an active one, and hasn't .. you know .. only been around in the last 5 or so years. Actually, 'the fold' is probably over a hundred years old as a term, incidentally, but I would have no idea how to prove it .. ("Above the fold", its Shakespeare, isn't it?)