This bit of newspaper jargon, "below the fold," means something on the front page below the folding across the middle of a broadsheet newspaper so it fits in a newspaper rack on the street corner. Which displays the top-half (above the fold) of the newspaper’s front page. The phrase is being used incorrectly in blogs. Strange that it would be used at all, actually.
In blogs, rare reader Veeshir tells me, it means to click on the "more" where the post stops on the front page. Which takes you "inside" to read the rest of the post. But, in newspaper jargon, that would be taking "the jump," to the "jump page" inside. So a blogger who wants to use the jargon correctly should say "after the jump" instead of "below the fold." But, given the (frequently justifiable) contempt that many bloggers have for newspapers, I don’t imagine the usage is any sort of homage. Maybe that’s why it’s been redefined.